Patent Description:
A head-up display, also referred to as a HUD, is a display system in which the viewer can maintain his viewing direction, because the contents to be displayed are displayed in his field of vision. While such systems, due to their complexity and costs, were originally mainly used in the aviation sector, they are now also being used in large scale in the automotive sector.

Head-up displays generally consist of an image generator, an optical unit and a mirror unit. The image generator generates the image to be displayed. The optical unit directs the image to the mirror unit. The image generator is often referred to as an imaging unit or PGU (Picture Generating Unit). The mirror unit is a partially reflecting, translucent pane. The viewer thus sees the content displayed by the image generator as a virtual image and at the same time the real world behind the translucent pane. In the automotive sector, the windscreen often serves as a mirror unit, the curved shape of which must be taken into account in the representation. Through the interaction of the optical unit and the mirror unit, the virtual image is an enlarged representation of the image generated by the image generator.

The image generator and the optical unit of a head-up display are typically arranged in a common housing assembly, which may also include electronic components necessary for operation of the head-up display. The housing assembly is sealed with a cover glass and protects the various components from damage as well as dust or other environmental influences. Furthermore, the housing assembly helps to simplify mounting of the head-up display in a vehicle, as all necessary components can be installed in a single production step.

The housing assembly usually consists of a lower housing and an upper housing, which are fastened to each other once all the necessary components of the head-up display have been mounted in their respective positions. The connection between the lower housing and the upper housing is at present typically realized using screws or rivets.

When the upper housing is fastened to the lower housing by screws or rivets, the housing assembly may suffer warpage and bending when it is exposed to higher temperatures, due to thermal expansion of the housing assembly. This may occur, for example, when a vehicle with a head-up display is parked in the sunlight. Such warpage and bending may cause defects in the displayed virtual image, which are not acceptable to a viewer.

<CIT> relates to an image generating unit for a head-up display and to a head-up display comprising such an image generating unit.

<CIT> relates to a head-up display for a motor vehicle for mounting in the dashboard area behind an instrument cluster, comprising a housing with functional components arranged therein or thereon.

<CIT> relates to the field of vehicle vision systems for viewing objects within and outside of a vehicle cabin.

<CIT> relates to a housing for a connector. The housing has a rectangular casing consisting of two parts, which are held together via spring clips. The two opposing sides of the casing have thickened wall sections to the left and right of the spring clips. These provide reception spaces for the latter. The spring clips have projecting hooked sections, which lock into corresponding openings in the cover.

It is an object of the present invention to provide an improved solution for a housing assembly that is suitable for an apparatus for generating a virtual image.

This object is achieved by a housing assembly according to claim <NUM>. The dependent claims include advantageous further developments and improvements of the present principles as described below.

According to one aspect of the invention, a housing assembly for an apparatus for generating a virtual image comprises a lower housing and an upper housing. The lower housing comprises support structures for installation of an image generator or an optical unit of the apparatus for generating a virtual image. The upper housing comprises a support surface configured to carry a cover glass. The upper housing is fastened to the lower housing by at least one flat metal spring clip. The flat metal spring clip is mounted on the housing assembly at respective fastening points of the lower housing and the upper housing.

As head-up displays are getting increasingly larger, the warpage and bending effects caused by thermal expansion, in particular the warping of the cover glass, are more likely to appear. Connecting the upper housing and the lower housing with flat metal spring clips has the advantage that the housing assembly is capable of compensating for thermal expansion. As a result, defects in the displayed image are eliminated to a large extent. Using a flat metal spring clip further has the advantage that the spring clip does hardly suffer any degradation by aging effects, e.g. due to an exposure to sunlight.

A further advantage is that the spring clips are easily mountable and demountable, both by hand or by using an automated process. In addition, the assembly using spring clips is simpler and cheaper than the assembly using screws.

When the upper housing and the lower housing are fastened by screws, typically self-tapping screws are used to eliminate the tapping process. On the one hand, this means that free particles are generated when the screws are fastened, which may cause the head-up display to fail during a cleanliness test. On the other hand, after mounting and demounting the screws for a couple of times, e.g. for accessing the components inside the housing for maintenance or repair, the threads are damaged. In contrast, the clips can be mounted and demounted repeatedly for hundreds of times without damaging the upper housing or the lower housing or generating any particles.

Also, in case of an assembly using rivets, a special tool is required for demounting the rivets. In addition, new rivets are needed for reassembly. This is not the case when spring clips are used.

In one advantageous embodiment, the at least one spring clip is made of an austenitic stainless steel. Preferably, the austenitic stainless steel is X10CrNi18-<NUM>, i.e. steel with <NUM>,<NUM> to <NUM>,<NUM> wt% (weight percent) Chrome and <NUM>,<NUM> to <NUM>,<NUM> wt% Nickel. This material is often used for springs, so that extensive knowledge about the design and properties of such springs exists.

In one advantageous embodiment, the spring force of the at least one spring clip is between <NUM> N and <NUM> N. It has been found that such values of the spring force ensure that the two parts of the housing assembly are securely connected. At the same time the values are sufficiently small to allow removing the spring clips, e.g. for repair of a component inside the housing assembly, with exertion of only a moderate force. The preferable spring force may depend on the type of spring clip that is used.

In one advantageous embodiment, a width of the at least one spring clip is between <NUM> and <NUM>. These values ensure that the desired spring force can easily be achieved. At the same time only a limited installation space is required for the spring clips, which gives greater flexibility for the design of the housing assembly.

In one advantageous embodiment, the upper housing is fastened to the lower housing by four spring clips. Using four spring clips for fastening the two parts of the housing assembly ensures that the housing assembly is tightly closed. At the same time the number of spring clips is sufficiently small to keep the time required for assembly relatively low, which reduces the overall cost of assembly.

In one advantageous embodiment, the upper housing is fastened to the lower housing by two spring clips each at or close to two opposite sides of the housing assembly. Preferably, the two opposite sides are the longer sides of the housing assembly. The thermal effects caused by the irradiation with sunlight are most pronounced along the longer sides of the housing assembly. Fastening the two parts of the housing assembly at or close to these longer sides ensures that thermally induced strain can be efficiently relaxed.

In one advantageous embodiment, the upper housing is fastened to the lower housing by two spring clips at one side of the housing assembly and one or more lugs hooking into corresponding holes at the opposite side of the housing assembly. This solution has the advantage that the number of parts to be assembled as well as the time required for assembly are reduced. As a consequence, the cost of assembly is likewise reduced.

According to one aspect of the invention, an apparatus for generating a virtual image comprises:.

Such an apparatus is advantageous in that it is relatively inexpensive to produce. At the same time, it is less susceptible to warpage and bending caused by thermal effects. The apparatus is hence well suited for use in an environment in which higher temperatures occur, e.g. in a motor transport vehicle.

According to one aspect of the invention, a vehicle comprises an apparatus according to the invention for generating a virtual image for a user of the vehicle. The vehicle may, for example, be a car or an aircraft. Of course, the inventive solution can also be used in other environments or for other applications, e.g. in trucks, busses, in railway and public transport, cranes and construction machinery, etc..

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

For a better understanding of the principles of the present invention, embodiments of the invention will be explained in more detail below with reference to the figures.

Like reference numerals are used in the figures for the same or equivalent elements and are not necessarily described again for each figure. It is to be understood that the invention is not limited to the illustrated embodiments and that the features described may also be combined or modified without departing from the scope of the invention as defined in the appended claims.

<FIG> shows a sketch of a state-of-the-art head-up display for a motor vehicle. The head-up display has an image generator <NUM>, an optical unit <NUM> and a mirror unit <NUM>. A beam SB1 emanates from a display element <NUM> of the image generator <NUM> and is reflected by a folding mirror <NUM> onto a curved mirror <NUM>, which reflects it in the direction of the mirror unit <NUM>. The mirror unit <NUM> is shown here as a windscreen <NUM> of the motor vehicle. From there, the SB2 beam is directed towards the eye <NUM> of an observer.

The observer sees a virtual image VI, which is located outside the vehicle above the bonnet or even in front of the vehicle. Due to the interaction of the optical unit <NUM> and the mirror unit <NUM>, the virtual image VI is an enlarged representation of the image displayed by the display element <NUM>. Here a symbolic speed limit, the current vehicle speed and navigation instructions are displayed. As long as the eye <NUM> is inside the eyebox <NUM> indicated by a rectangle, all elements of the virtual image are visible to the eye <NUM>. If the eye <NUM> is located outside the eyebox <NUM>, the virtual image VI is only partially or not at all visible to the viewer. The larger the eyebox <NUM> is, the less restricted the viewer is in his choice of the seating position.

The curvature of the curved mirror <NUM> is adapted to the curvature of the windscreen <NUM> and ensures that the image distortion is stable over the entire eyebox <NUM>. The curved mirror <NUM> is rotatably supported by a bearing <NUM>. By rotating the curved mirror <NUM>, it is possible to shift the eyebox <NUM> and thus to adjust the position of the eyebox <NUM> to the position of the eye <NUM>. The folding mirror <NUM> ensures that the distance travelled by the beam SB1 between the display element <NUM> and the curved mirror <NUM> is long, while at the same time the optical unit <NUM> remains compact. The optical unit <NUM> and the image generator <NUM> are accommodated in a housing assembly <NUM> and separated from the environment by a transparent cover <NUM>. The optical elements of the optical unit <NUM> are thus protected, for example, against dust inside the vehicle. An optical foil or polarizer <NUM> is located on the cover <NUM>. The display element <NUM> is typically polarized and the mirror unit <NUM> acts like an analyzer. The purpose of the polarizer <NUM> is, therefore, to influence the polarization such as to achieve a uniform visibility of the useful light. An anti-glare shield <NUM> serves to securely absorb light reflected across the interface of the cover <NUM> so that no glare is caused to the observer. In addition to sunlight SL, also light from another source of interference <NUM> might reach the display element <NUM>. In combination with a polarization filter, the polarizer <NUM> can also be used to suppress incident sunlight SL.

<FIG> shows a perspective view of a lower housing <NUM> of a housing assembly according to the invention. Depicted is a view into the inside of the lower housing <NUM>. In this embodiment, the housing assembly is fastened using four spring clips. Therefore, the lower housing <NUM> is provided with four fastening points <NUM>. Two fastening points <NUM> are located at a first side <NUM> of the lower housing <NUM>. A further fastening point <NUM> is located at a second side <NUM> opposite to the first side <NUM>. Due to constraints with regard to the available installation space, the fourth fastening point <NUM> is not located at the second side <NUM>, but close to this side <NUM>. In this embodiment, the first side <NUM> and the second side <NUM> are the longer sides of the housing assembly. Several alignment pins <NUM> are provided, which interact with corresponding alignment holes of the upper housing to facilitate alignment of the upper housing <NUM> and the lower housing during assembly. Inside the lower housing <NUM> a plurality of support structures <NUM> can been, e.g. for installation of the image generator or the optical unit.

<FIG> shows a perspective view of an upper housing <NUM> of a housing assembly according to the invention. Depicted is a view into the inside of the upper housing <NUM>. In addition to the four fastening points <NUM> for the spring clips, there are three alignment holes <NUM>, into which the corresponding alignment pins of the lower housing are inserted during assembly. An opening <NUM> is provided in the top side of the upper housing <NUM>. Light generated by the image generator and relayed by the optical unit leaves the housing assembly through this opening <NUM>.

<FIG> shows a top view of the upper housing <NUM> of <FIG>. As can be seen, the opening <NUM> is surrounded by a support surface <NUM>, which is designated by the hatched area. The purpose of the support <NUM> surface is to carry the cover glass and may be structured in order to improve the bonding properties when the cover glass is glued to the upper housing <NUM>.

According to above embodiment, the upper housing is fastened to the lower housing by four spring clips. It is, however, likewise possible to use two spring clips at one side of the housing assembly and one or more lugs hooking into corresponding holes at the opposite side of the housing assembly.

<FIG> shows a perspective view of a first embodiment of a spring clip <NUM> for fastening the upper housing and the lower housing. <FIG> shows a side view of this spring clip <NUM>. The spring clip <NUM> is preferably made of an austenitic stainless steel, e.g. X10CrNi18-<NUM>. The width of the spring clip <NUM> may, for example, be between <NUM> and <NUM>, whereas the height may be around <NUM>. Preferably, the thickness of the spring clip <NUM> is around <NUM>,<NUM>. The spring force of the spring clip <NUM>, which in this case is measured in the measurement direction D indicated by the arrow, is between <NUM> N and <NUM> N. Preferably, the spring force is <NUM> N. The spring force may be tuned by changing the various dimensions of the spring clip <NUM>, e.g. the curvature, the height or the depth.

<FIG> shows a side view of a second embodiment of a spring clip <NUM> for fastening the upper housing and the lower housing. Again, the spring clip <NUM> is preferably made of X10CrNi18-<NUM>. The width of the spring clip <NUM> may, for example, be between <NUM> and <NUM>, whereas the height may be around <NUM>. Preferably, the thickness of the spring clip <NUM> is around <NUM>,<NUM>. The spring force of the spring clip <NUM>, which in this case is measured in the measurement direction D indicated by the arrow, is between <NUM> N and <NUM> N. Preferably, the spring force is <NUM> N. The spring force may be tuned by changing the various dimensions of the spring clip <NUM>, e.g. the curvature, the height or the depth.

Claim 1:
A housing assembly (<NUM>) for an apparatus for generating a virtual image (VI), the housing assembly (<NUM>) comprising a lower housing (<NUM>) and an upper housing (<NUM>), wherein the lower housing (<NUM>) comprises support structures (<NUM>) for installation of an image generator (<NUM>) or an optical unit (<NUM>) of the apparatus for generating a virtual image (VI), and wherein the upper housing (<NUM>) comprises a support surface (<NUM>) configured to carry a cover glass, characterized in that the upper housing (<NUM>) is fastened to the lower housing (<NUM>) by at least one flat metal spring clip (<NUM>), which is mounted on the housing assembly (<NUM>) at respective fastening points (<NUM>) of the lower housing (<NUM>) and the upper housing (<NUM>).