Illumination – Illuminated scale or dial – Internal light source
Reexamination Certificate
2000-05-26
2001-05-01
Husar, Stephen (Department: 2875)
Illumination
Illuminated scale or dial
Internal light source
C362S084000, C362S489000
Reexamination Certificate
active
06224222
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims benefit of priority of Japanese Patent Applications No. Hei-8-198021 filed on Jul. 26, 1996 and No. Hei-9-134020 filed on May 23, 1997, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combined display panel for displaying various information thereon, and more particularly to a combined display panel in which a transparent display panel is disposed in front of a part of a surface of an instrument panel for use in an automotive vehicle, for example.
2. Description of Related Art
Combined display panels in which a transparent display panel such as a liquid crystal or electroluminescent display panel is disposed on the front surface of a usual instrument panel have been proposed hitherto. For example, Japanese Utility Model Publications No. Sho-55-16746 and No. Hei-3-17437 disclose a combined display panel having a transparent display panel of a liquid crystal or an a electroluminescent panel disposed in front of a conventional instrument. Display devices of this kind are able to display images displayed on the transparent panel in addition to images displayed on the conventional panel.
Japanese Patent Laid-Open Publication No. Hei-7-271310 discloses a combined display device of the same kind. This device turns off the display on a back panel when a front panel display is activated, and vice versa. In other words, images on the back and the front panels are selectively displayed. However, in an instrument panel of an automotive vehicle which displays various information on the same panel, including information such as vehicle speeds which have to be displayed always and information such as engine rotational speeds which are not necessary to be displayed always, it is not possible to turn off all the images displayed on the back or front panel. It is possible to overlap the front panel only on a part of the surface of the back panel where information which is not required to be displayed always is displayed, and to activate selectively the back and front panels. For example, a transparent front panel may be overlapped only on the surface of the back panel where a tachometer (engine speed indicator) is located and the surface of the back panel where a speedometer is located is left open without overlapping the front panel, and both images on the back and front panels may be selectively switched on or off.
In this case, however, there is a problem that luminance or brightness of the display device between the overlapped portion and the non-overlapped portion becomes different, because the transparent panel is not perfectly transparent but its transparency is usually less than 80%. This is because the transparent panel such as a liquid crystal or an electroluminescent panel is composed of many layers which are not perfectly transparent. The imbalance of luminance is harmful to a quality display.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide a combined display panel in which a front panel is overlapped only on a part of a back panel and luminance difference between the overlapped and non-overlapped portions is eliminated, and more particularly to provide a combined display panel having high display quality for an instrument panel of an automotive vehicle.
A transparent display panel such as an electroluminescent (EL) display panel is overlapped on a usual instrument panel to cover only a part thereof where information which is not required to be displayed always, such as a tachometer, is displayed. Displays shown on the EL panel and the overlapped portion of the instrument panel are selectively switched on or off. Under a normal and frequently occurring situation, only the instrument panel, i.e., the back panel is lit. In this case, there would be a luminance imbalance on the combined display panel between the overlapped and non-overlapped portions if the luminance of the instrument panel were uniform, because the transparency of the EL panel is not 100%. To eliminate the luminance imbalance on the combined display panel throughout a whole surface thereof, brightness of illuminating lamps for the back panel is made unequal between the overlapped and non-overlapped portions according to the present invention. That is, the brightness of the back lamps is made higher in the overlapped portion. The brightness of the back lamps may be adjusted without changing a brightness ratio between the overlapped and non-overlapped portions to attain an adequate luminance in accordance with an outside light while keeping a uniform overall luminance on the combined display panel.
Instead of making the back lamp brightness unequal, the overall luminance of the combined display panel may be made uniform by adding a filter for adjusting the luminance in front of the displays. A dimming filter which has different transparencies between the overlapped and non-overlapped portions may be placed to cover a whole front surface of the combined display panel. Also, a transparency adjustment filter may be placed to cover only the non-overlapped portion to attain an overall uniform luminance on the combined display panel.
The combined display panel may be also made by disposing an additional display panel on a part of a conventional instrument panel. In this case, to attain an overall uniform luminance on the combined display panel, a dimming filter covering a whole surface thereof, which has different transparencies in the area where the additional display panel is disposed and in the other area, may be used.
It is also possible to construct a combined display panel by placing two separate display surfaces so as not to overlap each other. When the two surfaces have different luminance, a transparency adjustment filter may be used to cover a brighter surface so that an overall luminance on the combined display panel is realized.
According to the present invention, luminance imbalance on the combined display panel is eliminated in various forms of the combined display panels, and a quality display can be realized.
REFERENCES:
patent: 5757127 (1998-05-01), Inoguchi
patent: 6120159 (2000-09-01), Inoguchi et al.
patent: 0775291 (1997-05-01), None
patent: 2266375 (1993-10-01), None
patent: 55-16746 (1980-04-01), None
patent: 55-39284 (1980-09-01), None
patent: 60-191079 (1985-12-01), None
patent: 61-11186 (1986-01-01), None
patent: 3-17437 (1991-04-01), None
patent: 7-271310 (1995-10-01), None
patent: 9-207625 (1997-08-01), None
Hattori Tadashi
Inoguchi Kazuhiro
Ito Nobuei
Denso Corporation
Husar Stephen
Pillsbury & Winthrop LLP
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