On-vehicle display device
BACKGROUND OF THE INVENTION 
     The present invention relates to a movable onvehicle large display device which can be employed for events such as a horse race, a bicycle race, a concert, a speech meeting and the like, all of which provide many people with image information in a large place. 
     Such an on-vehicle large display device is installed on the bed of a large vehicle, is moved to a place of a concert, a speech meeting or the like together with the vehicle and is installed therein. 
     FIG. 1 shows the arrangement of a conventional on-vehicle large display device. In FIG. 1, reference numeral 1 denotes a large vehicle, and reference numeral 2 denotes a display device installed on the bed 7 of the vehicle 1. The display device 2 comprises an upper screen 4 which can be vertically be moved by a vertical extension hydraulic unit 3, and a lower screen 6 which can be horizontally be moved by a horizontal extension hydraulic unit 5 (the left and right in the direction of movement of the vehicle are considered as the front and rear, respectively, hereinafter). 
     The operation of the device is described below. 
     FIG. 2A shows a housing state where the upper screen 4 is disposed in front of the lower screen 6. The display device 2 in this housing state is carried by the vehicle 1. When the display device 2 is constructed, the rod 3a of the vertical extension hydraulic unit 3 is first extended so that the upper screen 4 is upwardly moved, as shown in FIG. 2B. The lower screen 6 is then pushed forward by the rod 5a of the horizontal extension hydraulic unit 5 so as to be disposed below the upper screen 4, as shown in FIG. 2C. The upper screen 4 is moved slightly downward by the vertical extension hydraulic unit 3 so as to be mounted on the lower screen 6 to complete the assembly, as shown in FIG. 2D. The procedure for housing the assembled display device is reverse to that described above. 
     However, there is a demand for increasing the size of such an on-vehicle large display device. The conventional on-vehicle large display device has a limit with respect to an increase in the size thereof because of the assembly of the upper and lower screens. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an on-vehicle large display device which enables the construction of a very large screen. 
     In order to achieve the object, the present invention provides an on-vehicle large display device comprising an upper screen which can be vertically moved by a multistage extension hydraulic unit, an intermediate screen which can be diagonally moved upward and downward by a diagonal extension hydraulic unit and which is disposed below the upper screen upwardly moved, and a lower screen which can be moved horizontally by a horizontal extension hydraulic unit and which is disposed below the intermediate screen upwardly moved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic front view showing a conventional on-vehicle display device; 
     FIG. 2A is a schematic side view showing the state where the device shown in FIG. 1 is housed; 
     FIGS. 2B to 2D are schematic side views showing the process from the state where the device shown in FIG. 2A is housed to the state where the device is constructed; 
     FIG. 3 is a schematic front view showing an on-vehicle display device of the present invention; 
     FIG. 4 is a front view showing the state where the device shown in FIG. 3 is housed; 
     FIG. 5A is a schematic side view showing the state where the device shown in FIG. 3 is stored; and 
     FIGS. 5B to 5F are schematic side views showing the process from the state where the device shown in FIG. 5A is housed to the state where the same device is constructed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 shows the arrangement of an embodiment of the present invention. In FIG. 3, reference numeral 11 denotes a large vehicle; reference numeral 12, a display device; reference numeral 13, an upper screen; reference numeral 14, an intermediate screen; reference numeral 15, a lower screen; reference numeral 16, a multistage (two-state) extension hydraulic unit for vertically moving the upper screen 13; reference numeral 17, a diagonal extension hydraulic unit for diagonally moving the intermediate screen 14 upward and downward; and reference numeral 18, a horizontal extension hydraulic unit for horizontally moving the lower screen 15. The lower screen 15 is fixed to a bed 19 through a slide mechanism. FIG. 3 shows the state where the display device 12 configured as described above is assembled, and FIG. 4 shows the state where the device is housed. 
     The operation of the above embodiment is described below with reference to the assembly procedure shown in FIGS. 5A to 5E. FIG. 5A shows the state where the device is housed. In this state, the intermediate screen 14 and the lower screen 15 are disposed on the right and left sides, respectively, with the upper screen 13 therebetween. The display device 12 in the housing state is carried by the vehicle 11. Each of the upper, intermediate and lower screens 13, 14, 15 is formed in a thin shape so as to be mounted on the bed 19, as shown in the drawings. 
     When the display device 12 is constructed, the upper screen 13 is first lifted to the uppermost position by the two-stage rods 16a, 16b of the multistage extension hydraulic unit 16, as shown in FIG. 5B. As shown in FIG. 5C, the intermediate screen 14 is then diagonally moved upward, by the rod 17a of the diagonal extension hydraulic unit 17 which is fixed to the vehicle 11 so as not to fall, to a position slightly higher than the final position of the lower side of the upper screen 13. As shown in FIG. 5D, the lower screen 15 is then slid into the portion below the intermediate screen 14 by the rod 18a of the horizontal extension hydraulic unit 18. As shown in FIG. 5E, the intermediate screen 14 is then moved slightly downward so as to be mounted on the lower screen 15 by the rod 17a of the diagonal extension hydraulic unit 17. In the final stage, the upper screen 13 is moved slightly downward so as to be mounted on the intermediate screen 14 by the rod 16a of the multistage extension hydraulic unit 16 to complete the assembly of a large screen as one unit, as shown in FIG. 5F. The assembled screen may be returned to the housing state in accordance with the procedure reverse to that described above. 
     Assuming that the size of each of the screens 13, 14 and 15 is the same as that shown in FIG. 1, the assembled screen has the same width as that shown in FIG. 1 and a height of 1.5 times that shown in FIG. 1. An attempt can thus be made to further increase the size of the screen. Although the length of the vehicle 11 must be increased for increasing the width of the screen, the length can easily be increased. If the width of the screen is increased to 1.5 times, a large screen having a whole size of 2.55 times that shown in FIG. 1 can be obtained. 
     When the height is further increased, a screen may be further vertically divided into four parts, five parts . . . so as to be inserted between the uppermost screen and lowermost screen by a diagonal extension hydraulic unit having the same structure as that of the above diagonal extension hydraulic unit 17. 
     As described above, the embodiment of the present invention comprises the upper screen which can be vertically moved by the multistage extension hydraulic unit, the intermediate screen which can be diagonally moved upward and downward by the diagonal extension hydraulic unit and which is disposed below the upper screen upwardly moved, and the lower screen which can be horizontally moved by the horizontal extension hydraulic unit and which is disposed below the intermediate screen upwardly moved. The assembly of the upper, intermediate and lower screens can realize a screen larger than a conventional screen.