Abstract:
A display device is comprised of a main display panel, a transparent display panel that is disposed to cover the first display panel, and a control unit. The main display panel indicates a first information pattern, the transparent display panel indicates a second information pattern, and the control unit controls relative visibility of the main and transparent display panels to selectively indicate the first and second information patterns according to various vehicle conditions.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application relates to U.S. patent application Ser. No. 08/899,566 filed Jul. 24, 1997 and is based on and claims priority from Japanese Patent Application Hei 11-262304 filed Sep. 16, 1999, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device having a combined display-panel unit that is comprised of a main display panel and a transparent display panel overlapping the main display panel. 
     2. Description of the Related Art 
     JP-A-10-91087, which corresponds to U.S. patent application Ser. No. 09/899,566, and EP 0775 291 B1, which corresponds to JP-A-10-504101, disclose a vehicle combination meter having a front display panel that is comprised of a transparent electro-luminescent (EL) panel and a back display panel. When the back display panel displays an information pattern, the back display panel is illuminated while the front display panel is turned off to make the information patter visible. On the other hand, when the front display panel displays an information pattern, the illumination of the back panel is turned off. That is, the display is changed from one to another by turning on or off the illumination of the panels. 
     In the above combination meter, either one of the front and back panels can display the information pattern. If the information patterns are displayed by both panels concurrently, it is difficult for a viewer to recognize the information patterns correctly. 
     SUMMARY OF THE INVENTION 
     Therefore, a main object of the invention is to provide a display device having an improved combined-display-panel unit. 
     Another object of the invention is to provide a combined-display-panel unit that includes a main panel and a transparent panel, both of which can display clear information patterns concurrently. 
     According to a main aspect of the invention, a display device includes a main display panel, a transparent display panel disposed to cover the first display panel, and a control unit controlling relative visibility of the main and transparent displays to have a user selectively recognize information patterns displayed by both the display panels. Therefore, it is possible to indicate various information patterns by using any one of the panels or both panels, as the occasion demands. 
     According to another aspect of the invention, the control unit of the above display device controls luminance of at least one of the main and transparent display panels. Therefore, a user can easily recognize the level of importance or seriousness of the information. For this purpose, it is possible to increase the luminance of one of the display panel that indicates more important information patterns. It is also possible to increase the luminance for a predetermined period, and to change color or size of the transparent display. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: 
     FIG. 1 is an exploded diagram of a display device having a combined-display-panel unit according to a first embodiment of the invention; 
     FIG. 2 is a schematic cross-sectional plan view of the display device shown in FIG. 1; 
     FIG. 3 is a schematic cross-sectional side view of the display device shown in FIG. 1; 
     FIG. 4 is a schematic front view of the display device according to the first embodiment; 
     FIG. 5 is a schematic cross-sectional side view of an example of a self-illumination-type meter of the display device; 
     FIG. 6 is a schematic diagram of another example of the self-illumination-type meter of the display device; 
     FIG. 7 is a variation of the self-illumination-type meter; 
     FIG. 8A is a schematic cross-sectional view of a transparent EL display panel of a combined display-panel unit according to the first embodiment of the invention, and FIG. 8B is a variation thereof; 
     FIG. 9 is a block diagram of a luminance control unit of the display device according to the first embodiment; 
     FIG. 10 is an example of an information pattern displayed by the combined-display-panel unit according to the first embodiment; 
     FIGS. 11A,  11 B and  11 C illustrate examples of information patterns displayed by the combined-display-panel unit of a display device according to variations of the first embodiment; 
     FIG. 12 is a block diagram of a display device having a combined-display-panel unit according to a second embodiment of the invention; and 
     FIG. 13 illustrates an example of the display pattern displayed by the combined panel unit according to the second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A display device according to a first embodiment of the invention is described with reference to FIGS. 1-11A, B and C. 
     Display device  1  is a combination meter that includes a speedometer, tachometer, a fuel gauge, a cooling-water-temperature gauge, and an odometer. Illumination lamps  51 ,  52 ,  53  and  54  are disposed behind dial plate  3  to respectively illuminate the cooling-water-temperature gauge, the tachometer, the speedometer, and the fuel gauge. Indicators  41 ,  42 ,  43  and  44  of the cooling-water-temperature gauge, the tachometer, the speedometer, and the fuel gauge are respectively disposed at the front side of dial plate  3 . Dial plate- 3  is made of a transparent resinous plate with opaque scales and letters thereon. Indicators  41 ,  42 ,  43  and  44  are made of transparent resinous material. Drive units  61 ,  62 ,  63  and  64  respectively drive the indicators in response to signals from respective sensors (not shown). 
     The speedometer, the tachometer, the fuel gauge, the cooling-water-temperature gauge, and the odometer with dial plate  3 , indicators  41 ,  42 ,  43  and  44 , compose a self-illumination type combination meter. Dial plate  3 , indicators  41 ,  42 ,  43  and  44  respectively illuminate when illumination lamps  51 ,  52 ,  53  and  54  are turned on and darken when the illumination lamps are turned off. 
     In FIG. 2, illumination lamps  52  and  53  are ring-shaped fluorescent lamps, and lamps  51  and  54  are incandescent lamps. Light conduction members  10  are disposed to respectively correspond to illumination lamps  51 ,  52 ,  53  and  54 , so that light conduction members  10  can conduct portions of lights emitted from illumination lamps  51 ,  52 ,  53  and  54  to indicators  41 ,  42 ,  43  and  44 . The remainders of the lights emitted from illumination lamps  51 ,  52 ,  53  and  54  pass through the transparent portions of dial plate  3 . 
     As shown in FIG. 5, light conduction member  10  conducts the light emitted from lamp  5  to transparent indicator  4  to illuminate the same. Reference numeral  12  is a back panel, and reference numeral.  13  is a cap. 
     As shown in FIG. 6, it is possible to illuminate indicator  4  by the light emitted from LED  15 . As shown in FIG. 7, it is also possible to illuminate indicator  4  by fluorescent lamp  16  that is energized by an outside power source P.S. through a pair of electrodes  17 . 
     As shown in FIG. 8A, transparent EL display panel  2  is comprised of glass substratum  21 , an EL portion including elements  22 ,  23 ,  24 ,  25  and  26 , spacer  201 , and back plate  27 . Spacer  201  supports back plate  27  at a distance from glass substratum  21  to provide hermetically sealed space  202 , which is filled with silicone oil or the like. First and second transparent EL element  22  and  26  are transparent conductive films made from ITO (indium-tin oxide) or ZnO (zinc oxide). First and second insulation layers  23  and  25  are made from silicon nitride oxide, tantalum oxide and etc. Illumination layer  24  is made from zinc sulfide (as the host material). 
     EL display panel  2  can be a color display panel. As shown in FIG. 8B, color transparent EL display panel  2 ′ can be comprised of glass substratum  21 , an EL portion including elements  22 ,  23 ,  24   a ,  24   b ,  25  and  26 . First and second insulation layers  23  and  25  are made from silicon nitride oxide, tantalum oxide and etc. First (orange color) illumination layer  24   a  and second (green color) illumination layer  24   b  are disposed side by side on first insulation layer  23 . First illumination layer  24   a  is made from Zns:Mn, and second illumination layer  24   b  is made from Zns:Tb. First and second transparent EL element  22  and  26  are transparent conductive films made from ITO (indium-tin oxide) or ZnO (zinc oxide). An alternating voltage is applied by drive control circuit  72   a  across first transparent EL element  22  and second transparent EL element  26  so that first illumination layer  24   a  and second illumination layer  24   b  can illuminate in the respective colors. As a result, an ordinal message can be displayed in the green color, and a warning message can be displayed in the orange color. This operation is described in, for example, U.S. Pat. No. 5,989,785. 
     EL display panel  2  can be comprised of elements made from organic material. EL display panel  2  shown in FIG. 1 is disposed in front of the tachometer of display device  1  with circuit board  29  of a drive and control unit being disposed at the back thereof. El display panel  2  and circuit board  29  are connected to each other by flexible circuit board  28 . 
     Flexible circuit board  28  is soldered to first EL element at the right side of EL display panel  2  and to second EL element at the bottom of the same. As shown in FIGS. 2 and 3, flexible circuit board  28  extends from the right bottom of EL display panel  2  toward the back of display device  1  to be connected to circuit board  29  by a connector. 
     As shown in FIGS. 1 and 4, transparent EL display panel  2  overlaps or covers approximately a half of the front surface of display device  1  so that the front surface of display device  1  is divided to two sections,  3 A and  3 B. 
     As shown in FIG. 9, display device  1  has illumination lamps  51  and  52 , lamp-voltage control circuit  71 , drive control circuit  72 , luminance-level control circuit  73 , and vehicle information transmission system  74 . Luminance-level control circuit  73  controls lamp-voltage control circuit  7 i and drive control circuit  72 . Lamp-voltage control circuit  71  controls the luminance level of Illumination lamps  51  and  52 . Drive control circuit  72  controls voltage applied to illumination layer  24 , thereby controlling the luminance level of EL display panel  2 . Drive control circuit  72  includes a flash control circuit for flashing a message during a preset period. Luminance-level control circuit  73  receives signals and data from various sensors, such as a cooling-water temperature sensor, a seat-belt sensor, a gear-shift-position sensor, and a vehicle speed sensor. Luminance-level control circuit  73  determines the luminance levels of lamps  51  and  52  and EL display panel  2  according to the signals and data of vehicle information transmission system  74 . Luminance-level control circuit  73  sends lamp-voltage control circuit  71  and drive control circuit  72  to restore the luminance level to the original level after a preset time passes. 
     If a driver starts an engine of a vehicle equipped with the above described device without fastening a seat belt, luminance-level control circuit  73  receives an unfasten signal of a seat-belt sensor. Luminance-level control circuit  73  sends a control signal to lamp-voltage control circuit  71  and another unfasten control signal to drive control circuit  72 . Lamp-voltage control circuit  71  lowers the lamp voltage, thereby lowering the luminance levels of lamps  51  and  52 . Drive control circuit  72  controls transparent EL display panel  2  to flash a message “Please fasten seat belt” thereon, several times at a high luminance level, so that the message overlaps the display of the tachometer. 
     In the meanwhile, a normal person can clearly recognizes a signal if the ratio between a lower level luminance and a higher level luminance is 1.2 or more, and {square root over ( )}2 at optimum. 
     Therefore, the ratio between the lower luminance display by the tachometer and the higher luminance display of EL display panel is set to {square root over ( )}2, so that a driver can best recognize the message in a short time. 
     FIG. 10 shows an example of a warning message “Engine is overheating” on EL display panel  2 . This warning message is provided by substantially the same luminance control unit as that shown in FIG. 9 when the cooling-water-temperature sensor detects a temperature that is higher than a maximum level of the normal cooling-water temperature. Luminance-level control circuit  73  sends voltage control circuit  71  a control signal to lower the luminance level of the lamps and drive control circuit  72  a control signal indicating that the cooling-water temperature is higher than a maximum level of the normal cooling-water temperature. Voltage control circuit  71  lowers the luminance level of lamps  51  and  52 , and drive control circuit  72  controls transparent EL display panel to display message “Engine is overheating” at a luminance level higher than the luminance level of the tachometer or the cooling-water-temperature gauge. The ratio between the lower level luminance and the higher level luminance is {square root over ( )}2. The display of the message also overlaps the display of the tachometer. It is also possible to flash the message display. 
     Thus, when transparent EL display panel  2  displays a warning message related to the seat belt or engine overheating, the luminance level thereof is made higher than the luminance level of the tachometer and cooling-water-temperature gauge. Therefore, a driver can recognize the warning message very clearly. 
     It is possible to change the luminance level of EL display panel  2  according to the content of the information while the luminance levels of the tachometer and the cooling-water temperature-gauge are fixed. This can omit circuits for controlling the luminance levels of the tachometer and the cooling-water-temperature gauge. 
     Variations of the display device having a combined-display-panel unit according to the first embodiment of the invention is described with reference to FIGS. 11A,  11 B and  11 C. Each one of the variations is provided with substantially the same luminance control unit as that shown in FIG.  9 . However, the flash control circuit can be removed according to circumstances. As shown in FIG. 11A, EL display panel  2  displays letter “D” at the same luminance level as the tachometer and the cooling-water-temperature gauge. The letter “D” indicates that the shift lever is positioned at the drive range “D”. A driver can also see the tachometer and the cooling-water-temperature gauge through transparent EL display panel  2 . 
     When the shift lever is changed, a signal indicating the change of the shift lever is sent to luminance-level control circuit  73 . Consequently, luminance-level control circuit  73  sends voltage control circuit  71  a control signal to lower the luminance level and drive control circuit  72  to increase the luminance level thereof. Voltage control circuit  71  lowers the luminance level of lamps  51  and  52 , and drive control circuit  72  increases the luminance level of the transparent EL display panel  2  to a level higher than the luminance levels of the tachometer and the cooling-water-gauge. The above operation lasts several seconds after the shift lever changes. 
     Thus, the luminance level of EL display panel  2  is made higher than the luminance levels of a main display panel, such as a portion of dial plate  3  corresponding to the tachometer or the cooling-water-temperature gauge, if displayed information is important or changing. The luminance level of EL display panel  2  can be made equal to that of the main display panel if displayed information is not so important or is not changing. 
     FIG. 11B illustrates another variation of display by EL display panel  2 . A plurality of letters L,  2 ,  3 , D, N, R, P that correspond to positions of the shift lever is displayed at lower portion of EL display panel  2 . A driver can also see the tachometer and the cooling-water-temperature gauge through transparent EL display panel  2 . 
     In this arrangement, the displays of the main panel  1  and EL display panel  2  do not overlap each other, so that the luminance levels thereof can be made equal to each other. 
     FIG. 11C illustrates another variation of the display by EL display panel  2 . Enlarged letter D that corresponds to the D-range of the shift lever is displayed at the center of EL display panel  2  only when the shift lever is being changed to the D-range. 
     A display device having a combined-display-panel unit according to a second embodiment of the invention is described with reference to FIGS. 12 and 13. 
     The display device is comprised of combined panel unit  78 , LCD-panel drive-circuit  79 , EL-display-panel drive-circuit  80 , touch-panel control circuit  82 , system control circuit  81 , and radio-wave tuner  83 . Panel unit  78  includes liquid crystal display (LCD) panel  75 , transparent EL display panel  76 , and touch panel  77 , which are respectively connected to LCD-panel drive-circuit  79 , EL-display-panel drive circuit  80 , and touch-panel control circuit  82 . LCD-panel drive-circuit  79 , EL-display-panel drive circuit  80 , and touch-panel control circuit  82  are also connected to system control circuit  81 . Radio-wave tuner  83  is also connected to system control circuit. A driver can obtain various kinds of information such as character messages from outside radio stations by tuner  83  and system control circuit  81 . 
     EL display panel  76  is disposed in front of LCD panel  75 , and touch panel  77  is disposed close to the front surface of EL display panel  76 . If a driver touches a portion of touch panel  77 , a signal corresponding to the portion is sent from touch panel control circuit  82  to system control circuit  81 . 
     As shown in FIG. 13, LCD panel  75  displays a map, and transparent EL display panel  76  displays messages, menus, and switches of TV set and others. If a user touches a portion of touch panel  77  overlapping one of the switches displayed on transparent EL display panel  76 , a signal corresponding to the touched portion is sent from touch panel control circuit  82  to system control circuit  81 . System control circuit  81  sends control signals corresponding to the touched portion to LCD-panel drive-circuit  79  and EL-display panel drive-circuit  80 . For example, if the user touches a portion corresponding to a switch of a TV set, the display of LCD panel  75  changes to a TV program from something like a map. The display of switches on EL display panel  76  can be changed according to the display pattern of LCD panel  75 . 
     Usually, the luminance level of displays of menus, maps, TV programs by EL display panel  76  is set lower than the luminance level of the display by LCD panel  75 , so that a user can recognize a map on LCD panel  75  easily. When the user touches a specific portion of touch panel  77  corresponding to a switch that is displayed by EL display panel  76 , the luminance level of the touched portion increases to a level higher than the luminance level of LCD panel  75 . Therefore, the user can recognize the touched portion very easily. 
     It is possible to provide a switch-that is not usually displayed by EL display panel  76  but is only displayed when a finger of the user is detected its access to the switch by means of an infrared light sensor or the like. It is also possible for EL display panel  76  to display broadcasted character messages. For example, if system control circuit  81  receives a broadcasted message “TRAFFIC JAM DUE TO ACCIDENT:  15  KM”, it sends a control signal to LCD-panel drive-circuit  79  to lower the luminance level of LCD panel  75  and a control signal to EL-display-panel drive-circuit  80  to make EL display panel  76  display the same message at a luminance level higher than that of LCD panel  75 . As shown in FIG. 13, a portion of a map can be omitted to make the message clearer. 
     As a variation of the above embodiments, a plurality of transparent EL displays can be provided with a display device. It is also possible to provide a single EL display panel that overlaps a plurality of display panels. 
     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than restrictive, sense.