Abstract:
An exterior mirror assembly with an optical display is suggested, whereby a light opening ( 2 ) is provided on the exterior mirror assembly for the passage of light of a warning display. The optical display comprieses of a display housing ( 4 ), into which an active illuminated display element ( 10 ) is mounted as a light source.

Description:
[0001]    The invention relates to an exterior mirror with an optical display device with at least one light source and a control unit, which is assigned to an assistance system. 
       PRIOR ART 
       [0002]    Motor vehicles with assistance systems such as a lane change assistance system are known in DE 103 18 741 A1. In the process, one or several sensors monitor the surroundings of the vehicle at the sides and at the rear. A control unit calculates whether an upcoming lane change could result in a hazardous situation. If there is a high degree of danger, an optical display device, usually an LED, is triggered on the exterior mirror, which should give an indication of the danger. Thereby, it is intended that the hazardous situation is continually reproduced by the optical display means. 
         [0003]    However, systems of this type have the disadvantage that the perceptibility of the optical signal is not guaranteed in different ambient light conditions. A fixed, pre-determined light intensity can lead to irritating the driver in darkness, and in contrast, cannot be detected at all in bright sunshine. A solution is known in DE 10 2005 038 179 B4, in which the brightness of the light source can be changed by the control unit, depending on a measurand provided to the control device, showing a measurement for the ambient brightness. 
         [0004]    Instead of operating with a pre-determined brightness, the display here adapts to the current ambient brightness. This means that in the case of relatively dark surroundings, the light source of the optical display device only illuminates very weakly, so that whilst the display can still clearly be seen with a glance in the direction of the exterior mirror, it does not irritate or even dazzle. In very bright surroundings, for example, in bright sunshine, the light source then accordingly illuminates brightly, so that its light is not covered by the sunlight. The optical perceptibility is therefore adapted to the needs of the driver. 
         [0005]    No optical solution is suggested in addition to this. In optical displays, there is also always the problem that the display surface should be illuminated homogeneously, and in the case of use in a motor vehicle, should also harmoniously fit into the external contour of the vehicle. 
         [0006]    The object of the invention is to create an optical display, which meets the high demands of a variable, homogeneously illuminated display. 
     
    
     
       DESCRIPTION OF THE INVENTION 
         [0007]    The object is achieved by the use of display technology. The subsequent description explains the realization of the solution according to the invention by means of exemplary embodiments. 
           [0008]      FIG. 1  shows a typical mounting location. 
           [0009]      FIG. 2  shows a display in the prior art as an exploded view. 
           [0010]      FIG. 3  shows a cut through a display in the prior art. 
           [0011]      FIGS. 4 and 5  show a display according to the invention. 
           [0012]      FIG. 6  shows an alternative embodiments. 
           [0013]      FIG. 7  shows lighting behind mirror glass. 
       
    
    
       [0014]    Optical displays on and in the exterior mirror must be installed in a position, which allows the driver to see the display. Since it is disadvantageous if the beam path of the optical display must be laboriously diverted, advantageous installation positions are available on and in the mirror base, or in the region of the mirror housing, which extends close to the vehicle. An exemplary arrangement is shown in  FIG. 1 . A part of an exterior mirror assembly can be seen here, consisting of a mirror base—not shown here—and a mirror head pivotably mounted thereto. 
         [0015]      FIG. 1  shows a housing cover  1 , which at least partly surrounds the mirror head. The mirror cover  1  comprises several openings, firstly for receiving the mirror glass, which is mounted on a holder with or without an adjustment motor, as well as an opening for a direction-indicator lamp on the side turned away from the mirror glass. Furthermore, the housing cover  1  comprises an opening  2  for receiving an optical display. 
         [0016]    In the example described, the opening  2  is formed by a material recess. A variant can also be implemented in another embodiment, in which the opening  2  for the optical display is a light opening, and the material in this position consists of transparent or semi-transparent material. Light openings of this type can be produced by two-component injection molding. 
         [0017]      FIG. 2  shows the design of an optical display as used in the prior art. 
         [0018]    A housing cap  3  closes a display housing  4  to a closed module, which is installed in this configuration. A closed module means a structural configuration; the module does not have to be hermetically sealed against environmental influences such as moisture and dust. The light sources are situated on a board  6  within the display housing  4 . This here concerns four LEDs  5 , which are mounted equidistantly, in order to achieve illumination, which is as even as possible, of the optical display. A collecting lens, here specifically a Fresnel lens, which is mounted or integrated on the upper side of a hollow body, is situated in the beam path of the LEDs. An optical lens  9  optimizes the emission characteristics of the optical display. If necessary, the optical lens and the collecting lens can also be accommodated in an optical component. An external cover pane  8  is situated above this, which is adapted to the geometry and size of the opening  2 , and is sealed with a sealing ring, in order to prevent the entry of dust and moisture. 
         [0019]    The use of LEDs is common in the prior art, but other light sources are also possible for the backlighting. EL foils or OLEDs as well as their further developments are used. To this end, the number of light sources and their arrangement depends on the respective display. 
         [0020]      FIG. 3  shows this design again in a sectional view. Despite the effort, homogeneous illumination of the external cover pane  8  is not achieved with a Fresnel lens and an optical lens. Brightness focus points of the LEDs can still be detected from the outside. 
         [0021]    In addition, at a suitable angle, the LEDs and the printed circuit board can be seen through the cover pane. 
         [0022]      FIG. 4  shows a design for an optical display with an optically active element, for example, an LCD element  10 . As a light source, no individual LEDs are used on a board, but a background lighting which with the current prior art rather achieves complete lighting for liquid crystal cells or displays. In the display according to the invention, LCD cells with integrated lighting are used, as they are used in large quantities in mobile telephones. The LCD element  10  is mounted into the display housing  4  and electrically contacted. In the example of  FIG. 4 , another additional optical lens is present, which is covered by the external cover pane  8 . In order to simplify the design, the optical lens is not present in  FIG. 5 . The LCD element is covered by the external cover pane. 
         [0023]    Various possibilities are available for receiving the display, which are already known from the prior art of display attachments in instrument clusters inside the vehicle. The display is not permitted to be installed with high stain, since otherwise there is the risk of destruction of the functionality of the display. There is also the possibility of implementing the display in an injection molding process, and therefore to produce a two-component part from the display and the plastic housing. The two-component element can also be expanded to a three-component element, in which the cover pane is also applied. The LCD element  10  consists of pixels, which, in the simplest case, all have the same color. The control typically takes place in the prior art with the so-called matrix control by control of individual lines horizontally and vertically, which thus makes it possible to switch on or off individual pixels, and therefore to selectively control the light through the display per pixel. It is also possible to design the display control in such a way that in the controlled state, all pixels are simultaneously active or inactive, so that the element is completely illuminated. A colored configuration is also possible when using LCD elements. In addition, the color for the warning display can be varied, in order to achieve gradual increments of the hazard warning. When using LCD cells, information symbols as in a conventional display can also be generated. 
         [0024]    As an active optical element of first choice, liquid crystal displays are suitable due to their sophisticated development state and their qualities. Liquid crystals are organic compounds, which have the characteristics of liquids as well as the characteristics of solid bodies. A simple liquid crystal display element consists of the “Schadt-Helfrich cell”: The inner sides of two glass plates are coated with a transparent electrode layer, with the liquid crystal situated in between. The molecules are arranged in a pre-determined direction, parallel to the surface coated with a polyamide and brushed in a preferred direction. In addition, both external plates are coated with polarization filters rotated 90 degrees to one another. The result of this is that the liquid crystals are arranged helically, with a helix twisted 90 degrees being known as a TN=Twisted Nematic. 
         [0025]    The incident light from background lighting is polarized before entry into the liquid. Due to the twisting of the molecule surfaces, a rotation of the polarization direction of the light takes place. In turn, this results in the light being able to pass the opposing filter, and the cell shines brightly. In an idle state, the display is transparent; this arrangement is also named normally white mode. 
         [0026]    If an electrical voltage is applied to the electrodes, a rotation of the molecules also occurs under the influence of the electrical field, so that they are orientated perpendicularly to the electrode surfaces. The twisting is thus cancelled, the polarization direction of the light is no longer changed, and therefore it cannot pass the second polarization filter. 
         [0027]    The inverse function is expedient for the use as an optical display: If the polarization filters are arranged in parallel, the cell is dark without voltage and bright with voltage. This is normally black mode. This design is usually not used in display technology due to poor contrast ratios. However, it is well suited for the optical display. A display can theoretically consist of any number of cells of this type. In a TFT monitor, three cells together show a color pixel. 
         [0028]    In STN displays (Super Twisted Nematic), the twist angle of the molecules is increased to 180-270°. Therefore, a higher contrast than with usual TN displays can be achieved. These displays are also named blue mode LCDs, since color shifts occur due to the dichroism: In the process, white becomes reddish to orange. This design and also the color shift can be advantageously used for the optical display. In many cases, the optical displays should warn in shades of red, so color compensation is not at all desirable. 
         [0029]    For use in the automotive industry as an optical display, the ‘Double Super Twisted’ DSTN technology comes into question, which is mass-produced. If an electrical field lies on the active cell, then the linear polarized light passes smoothly through from the rear polarizer without being changed. Circular polarization first takes place in the passive cell. Because circularly polarized light is not retained by the polarizers, the screen is bright at this point. Through exact alignment of the materials used, as well as the cell dimensions, the light passing through becomes white. The complex design of a DSTN liquid crystal cell involves relatively high effort in its production. A new process is therefore developed, which leads to flatter displays with lower weight. This new solution is named triple supertwisted nematic LCD (TSTN). There is only one STN-LC cell. The color interferences of normal STN technology are counterbalanced by two special films, which are applied—between the polarizer and glass—in front of and behind the cell. These films are responsible for another name of this technology: FST, “Film-Supertwisted”. The considerably improved contrast, the lower weight, the flatter and less laborious construction methods have made TSTN-LC displays possible as a mass product. 
         [0030]    The statements on the LCD cell should not limit the invention to the use of a cell of this type. Any other actively illuminated cell which can be actively controlled, such as an OLED (organic LED) or AMOLED (Active Matrix Organic LED) cell, can be used. Only the element must be robust enough for outdoor use on the vehicle. The cell in the optical display must simply be an active illuminated cell. LEDs, which emit into a diffuser plate at the side, are used as background lighting in commercial LCDs. The light is homogeneously coupled into the actual liquid crystal cells by optical films. 
         [0031]      FIGS. 6 and 7  show alternative solutions for the optical display. In the prior art, lighting modules are already known, whose light shines through a mirror glass in the direction of the driver. For this purpose, the mirroring layer is removed extensively or in the form of signs. The lighting element is applied behind the mirror glass. 
         [0032]      FIG. 6  shows a mirror glass  11 , into which signs  12  are introduced. The mirror glass is adhered onto a backing plate  13 . The optical display is situated as backlighting of the sign in the region of the signs in the mirror glass. In this case, the optical display is either adhered to the rear side as a separate module, or is structurally integrated into the backing plate, which is connected to the mirror glass. 
         [0033]    The design of the optical display corresponds to the design according to  FIG. 4 . 
         [0034]    A housing cap  3  closes a display housing  4  to a closed module, which is installed in this form. The light sources, the LCD element  10 , are situated within the display housing  4 . An optical pane  9  closes the display housing, which is directly connected to the mirror glass  11 .