1. Field of the Invention
The present invention relates to a combiner (half transparent reflector) reflecting an image supplied from an on-vehicle display so that a driver can see a virtual one of the displayed image. The invention also relates to an on-vehicle display unit having the combiner as well as a manufacturing method of the combiner.
2. Related Art
Such on-vehicle display units are generally called as a heap-up display. The heap-up display can superpose additional information required for operation of a motor vehicle and a foreground of the vehicle so that a driver can see the information with little turn of his eye during the operation of the vehicle.
FIG. 12 is a general constitutional view showing a conventional on-vehicle display unit of such a type. In FIG. 12, the on-vehicle display unit has a display 2 disposed in an instrument panel 8 positioned under a windshield 7 of a motor vehicle. The display 2 is provided with a displaying device 3 having a screen facing upward. A displayed image of the displaying device 3 passes through a prism assembly 4 and a pair of polarizer plates 5 and 6 and is reflected by a combiner 1 so that a virtual one I of the displayed image can be seen by a driver's eye E. The prism assembly 4 consists of a first prism 4a and a second prism 4b which are disposed close to each other, and the first prism 4a has a vertex oriented opposite to that of the second prism 4b. The polarizer plate 5 has a polarizing axis perpendicular to that of the polarizer plate 6.
The combiner 1 used in the on-vehicle display unit of FIG. 12 has a reflector film fitted on a resin base with a transparent adhesive, and the polarizer plate 6 is fitted to the combiner 1 with a transparent adhesive.
However, the combiner 1 is configured not only in a flat plate but also in a concave shape for positioning the virtual image I with a longer distance from the driver's eye. Thereby, the driver can see the virtual image I and a foreground of the vehicle simultaneously with ease. It has been a difficult work to precisely fit a reflector film on the concave surface.
The transparent adhesive for binding the resin base and the reflector film as well as for binding the combiner 1 and the polarizer plate 6 disadvantageously tends to decease transparency thereof under a hot and high humidity atmosphere.
The combiner 1 and the polarizer plate 6 are formed in separate bodies, which increases a manufacturing cost thereof.