Patent Publication Number: US-2021195774-A1

Title: Foldable display device

Description:
FIELD OF INVENTION 
     The present disclosure relates to the technical field of display devices, and particularly to a foldable display device. 
     BACKGROUND 
     Flexible display panels, such as organic light emitting diode display panels, are used to implement foldable display devices due to their flexibility. 
     However, when a current foldable display device is in an unfolded state, a foldable display area in a center of its flexible display panel is not supported. Therefore, when a finger presses the foldable display area for touch control, the foldable display area is prone to collapse. Furthermore, the foldable display area is also prone to wrinkle after being bent several times, thereby causing peeling. Therefore, it is necessary to provide a foldable display device to solve the problems existing in the prior art. 
     SUMMARY OF DISCLOSURE 
     In order to solve the technical problems that the foldable display area of the current foldable display device is prone to collapse due to finger pressing or wrinkle and peeling due to bending, the present disclosure provides a foldable display device. The foldable display device comprises a flexible display panel, a first bottom shell, a second bottom shell, a lifting mechanism, and a transmission mechanism. The flexible display panel comprises a first display area, a second display area, and a foldable display area between the first display area and the second display area. The first bottom shell is disposed below the first display area. The second bottom shell is disposed below the second display area. The lifting mechanism comprises a support member, a first support rod, a second support rod, a third support rod, and a fourth support rod. The support member is disposed below the foldable display area. Top ends of the first support rod and the third support rod are rotatably connected to a first side of the support member. Top ends of the second support rod and the fourth support rod are rotatably connected to a second side of the support member. The second side is opposite to the first side. The first support rod intersects the second support rod, and the third support rod intersects the fourth support rod. The transmission mechanism is connected to bottom ends of the first support rod, the second support rod, the third support rod, and the fourth support rod, the first bottom shell, and the second bottom shell. The transmission mechanism is configured to apply a moment to the first support rod, the second support rod, the third support rod, and the fourth support rod during a unfolding process of the foldable display device so that the support member provides support for the foldable display area when the foldable display device is in an unfolded state. 
     In a first embodiment, the support member is a rigid plate. During the process of unfolding the foldable display device, the transmission mechanism makes the bottom end of the first support rod close to the bottom end of the second support rod and makes the bottom end of the third support rod close to the bottom end of the fourth support rod. Therefore, the support member is raised in parallel with respect to the first bottom shell and the second bottom shell to a position providing support for the foldable display area. 
     In the first embodiment, the transmission mechanism comprises a first bottom rod, a second bottom rod, a first rack, a second rack, a third rack, a fourth rack, a first gear, a second gear, a third gear, and a fourth gear. Both ends of the first bottom rod are respectively connected to the bottom end of the first support rod and the bottom end of the third support rod. Both ends of the second bottom rod are respectively connected to the bottom end of the second support rod and the bottom end of the fourth support rod. The second bottom rod is parallel to the first bottom rod. The first rack is connected to one end of the first bottom rod. The second rack is connected to the other end of the first bottom rod. The third rack is connected to one end of the second bottom rod. The fourth rack is connected to the other end of the second bottom rod. The first gear is connected to an end of a side of the second bottom shell facing the first bottom shell. The first gear is disposed on and meshes with the first rack. The second gear is connected to the other end of a side of the second bottom shell facing the first bottom shell. The second gear is disposed on and meshes with the second rack. The third gear is connected to an end of a side of the first bottom shell facing the second bottom shell. The third gear is disposed on the third rack and meshes with the third rack and the first gear. The fourth gear is connected to the other end of a side of the second bottom shell facing the first bottom shell. The fourth gear is disposed on the fourth rack and meshes with the fourth rack and the second gear. 
     In the first embodiment, during the unfolding process of the foldable display device, the first gear and the third gear rotate synchronously to bring the first rack and the third rack approach each other, and the second gear and the fourth gear rotate synchronously to bring the second rack and the fourth rack approach each other. Therefore, the first bottom rod and the second bottom rod approach each other, the bottom end of the first support rod and the bottom end of the second support rod approach each other, the bottom end of the third support rod and the bottom of the fourth support rod approach each other, and the support member is raised in parallel with respect to the first bottom shell and the second bottom shell to a position providing support for the foldable display area. 
     In the first embodiment, the foldable display device further comprises a gear cover. The gear cover comprises a cover plate, two side plates, and two sliding grooves. The cover plate covers the lifting mechanism. The two side plates are respectively disposed on two opposite sides of the cover plate. The first gear and the third gear are rotatably connected to one side plate. The second gear and the fourth gear are rotatably connected to the other side plate. The two sliding grooves are respectively disposed on the cover plate near the two side plates. One of sliding grooves is configured for the first rack and the third rack to slide therein, and the other sliding groove is configured for the second rack and the fourth rack to slide therein. 
     In the first embodiment, the foldable display device further comprises a first middle frame and a second middle frame. The first middle frame is disposed between the first bottom shell and the first display area. The first middle frame is configured to support the first display area when the foldable display device is in the unfolded state. The second middle frame is disposed between the second bottom shell and the second display area. The second middle frame is configured to support the second display area when the foldable display device is in the unfolded state. 
     In the first embodiment, the foldable display device further comprises a first front frame and a second front frame. The first front frame is disposed on the first display area and surrounding the first bottom shell. The second front frame disposed on the second display area and surrounding the second bottom shell. 
     In a second embodiment, an intersection of the first support rod and the second support rod is provided with a hinge, and an intersection of the third support rod and the fourth support rod is provided with another hinge. The support member is a rigid plate provided with four chutes. The top ends of the first support rod, the second support rod, the third support rod, and the fourth support rod are rotatably connected to the support member via the four chutes, respectively. During the unfolding process of the foldable display device, the transmission mechanism makes the top ends of the first support rod and the second support rod approach each other through the chutes and makes the top ends of the third support rod and the fourth support rod approach each other through the chutes. Therefore, the support member is raised in parallel with respect to the first bottom shell and the second bottom shell to a position providing support for the foldable display area. 
     In the second embodiment, a ratio of a distance from the top end of the first support rod to the adjacent hinge to a distance from the bottom end of the first support rod to the same hinge, a ratio of a distance from the top end of the second support rod to the adjacent hinge to a distance from the bottom end of the second support rod to the same hinge, a ratio of a distance from the top end of the third support rod to the adjacent hinge to a distance from the bottom end of the third support rod to the same hinge, and a ratio of a distance from the top end of the fourth support rod to the adjacent hinge to a distance from the bottom end of the fourth support rod to the same hinge are greater than 0 and less than or equal to 1. 
     In the second embodiment, the transmission mechanism comprises a first bottom rod, a second bottom rod, a first rack, a second rack, a third rack, a fourth rack, a first gear, a second gear, a third gear, and a fourth gear. Both ends of the first bottom rod are respectively connected to the bottom end of the first support rod and the bottom end of the third support rod. Both ends of the second bottom rod are respectively connected to the bottom end of the second support rod and the bottom end of the fourth support rod. The second bottom rod is parallel to the first bottom rod. The first rack is connected to one end of the first bottom rod. The second rack is connected to the other end of the first bottom rod. The third rack is connected to one end of the second bottom rod. The fourth rack is connected to the other end of the second bottom rod. The first gear is connected to an end of a side of the second bottom shell facing the first bottom shell. The first gear is disposed on and meshes with the first rack. The second gear is connected to the other end of a side of the second bottom shell facing the first bottom shell. The second gear is disposed on and meshes with the second rack. The third gear is connected to an end of a side of the first bottom shell facing the second bottom shell. The third gear is disposed on the third rack and meshes with the third rack and the first gear. The fourth gear is connected to the other end of a side of the second bottom shell facing the first bottom shell. The fourth gear is disposed on the fourth rack and meshes with the fourth rack and the second gear. 
     In the second embodiment, during the unfolding process of the foldable display device, the first gear and the third gear rotate synchronously to bring the first rack and the third rack approach each other, and the second gear and the fourth gear rotate synchronously to bring the second rack and the fourth rack approach each other. Therefore, the first bottom rod and the second bottom rod approach each other, the bottom end of the first support rod and the bottom end of the second support rod approach each other, the bottom end of the third support rod and the bottom of the fourth support rod approach each other, and the support member is raised in parallel with respect to the first bottom shell and the second bottom shell to a position providing support for the foldable display area. 
     In a third embodiment, an intersection of the first support rod and the second support rod is provided with a hinge, and an intersection of the third support rod and the fourth support rod is provided with another hinge. The support member is a flexible plate. During the unfolding process of the foldable display device, the transmission mechanism makes the top end of the first support rod away from the top end of the second support rod and makes the top end of the third support rod away from the top end of the fourth support rod. Therefore, the support member is unfolded to provide support for the foldable display area. 
     In the third embodiment, a ratio of a distance from the top end of the first support rod to the adjacent hinge to a distance from the bottom end of the first support rod to the same hinge, a ratio of a distance from the top end of the second support rod to the adjacent hinge to a distance from the bottom end of the second support rod to the same hinge, a ratio of a distance from the top end of the third support rod to the adjacent hinge to a distance from the bottom end of the third support rod to the same hinge, and a ratio of a distance from the top end of the fourth support rod to the adjacent hinge to a distance from the bottom end of the fourth support rod to the same hinge are greater than 0 and less than or equal to 1. 
     In the third embodiment, the transmission mechanism comprises a first bottom rod, a second bottom rod, a first rack, a second rack, a third rack, a fourth rack, a first gear, a second gear, a third gear, and a fourth gear. Both ends of the first bottom rod are respectively connected to the bottom end of the first support rod and the bottom end of the third support rod. Both ends of the second bottom rod are respectively connected to the bottom end of the second support rod and the bottom end of the fourth support rod. The second bottom rod is parallel to the first bottom rod. The first rack is connected to one end of the first bottom rod. The second rack is connected to the other end of the first bottom rod. The third rack is connected to one end of the second bottom rod. The fourth rack is connected to the other end of the second bottom rod. The first gear is connected to an end of a side of the second bottom shell facing the first bottom shell. The first gear is disposed below and meshes with the first rack. The second gear is connected to the other end of a side of the second bottom shell facing the first bottom shell. The second gear is disposed below and meshes with the second rack. The third gear is connected to an end of a side of the first bottom shell facing the second bottom shell. The third gear is disposed below the third rack and meshes with the third rack and the first gear. The fourth gear is connected to the other end of a side of the second bottom shell facing the first bottom shell. The fourth gear is disposed below the fourth rack and meshes with the fourth rack and the second gear. 
     In the third embodiment, during the unfolding process of the foldable display device, the first gear and the third gear rotate synchronously to bring the first rack and the third rack away from each other, and the second gear and the fourth gear rotate synchronously to bring the second rack and the fourth rack away from each other. Therefore, the first bottom rod and the second bottom rod each other, the bottom end of the first support rod and the bottom end of the second support rod away from each other, the bottom end of the third support rod and the bottom of the fourth support rod away from each other, and the support member is unfolded to provide support for the foldable display area. 
     In the third embodiment, when the foldable display device is in a folded state, the flexible plate is bent and accommodated in a space defined by the first support rod, the second support rod, the third support rod, and the fourth support rod from their top ends to their adjacent intersections. When the foldable display device is in an unfolded state, the flexible plate is in an unfolded state. 
     In the third embodiment, the flexible plate is made of a flexible material or a plurality of rigid strips connected together by a rotating shaft. 
     When a foldable display device of the present invention is in an unfolded state, a support member of a lifting mechanism provides support for a foldable display area by a transmission mechanism. This prevents the foldable display area from collapsing due to finger pressing, or wrinkling and peeling due to bending. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a foldable display device according to a first embodiment of the present invention in an unfolded state. 
         FIG. 2  is a schematic diagram of the foldable display device according to the first embodiment of the present invention in a folded state. 
         FIG. 3  is an exploded view of the foldable display device according to the first embodiment of the present invention in the unfolded state, in which sliding grooves are omitted. 
         FIG. 4  is a partially exploded view of the foldable display device according to the first embodiment of the present invention in the folded state. 
         FIG. 5  is a schematic diagram showing a combination of a first bottom shell, a second bottom shell, a first front frame, a second front frame, a lifting mechanism, and a transmission mechanism according to the first embodiment of the present invention; 
         FIG. 6  is a partially enlarged view of an X region in  FIG. 5 . 
         FIG. 7  is a schematic diagram of the foldable display device according to the first embodiment of the present invention in the folded state, in which a gear cover is omitted. 
         FIG. 8  is a partially enlarged view of a Y region in  FIG. 7 . 
         FIG. 9  is a schematic diagram of the lifting mechanism and the transmission mechanism according to the first embodiment of the present invention when the foldable display device is in the unfolded state, in which gears are omitted. 
         FIG. 10  is a schematic diagram of the lifting mechanism and the transmission mechanism according to the first embodiment of the present invention when the foldable display device is in the folded state, in which the gears are omitted. 
         FIG. 11  is a schematic diagram of a lifting mechanism and a transmission mechanism according to a second embodiment of the present invention when a foldable display device is in an unfolded state, in which gears are omitted. 
         FIG. 12  is a schematic diagram of the lifting mechanism and the transmission mechanism according to the second embodiment of the present invention when the foldable display device is in a folded state, in which the gears are omitted. 
         FIG. 13  is a schematic diagram of a lifting mechanism and a transmission mechanism according to a third embodiment of the present invention when a foldable display device is in a folded state, in which gears are omitted. 
         FIG. 14  is a schematic diagram of the lifting mechanism and the transmission mechanism according to the third embodiment of the present invention when the foldable display device is in an unfolded state, in which the gears are omitted. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of various embodiments of the present disclosure with reference to the accompanying drawings is used to illustrate specific embodiments that can be practiced. Directional terms mentioned in the present disclosure, such as “above”, “below”, “front”, “back”, “left”, “right”, “inside”, “outside”, “side”, are merely used to indicate the direction of the accompanying drawings. Therefore, the directional terms are used for illustrating and understanding the present disclosure rather than limiting the present disclosure. In the figures, elements with similar structures are indicated by the same reference numerals. 
     Please refer to  FIG. 1  to  FIG. 10 . A foldable display device  11  according to a first embodiment of the present invention comprises a flexible display panel  500 , a first bottom shell  100 , a second bottom shell  200 , a lifting mechanism, and a transmission mechanism. The flexible display panel  500  may be an organic light emitting diode display panel. The flexible display panel  500  comprises a first display area  510 , a second display area  520 , and a foldable display area  530  between the first display area  510  and the second display area  520 . The first display area  510 , the second display area  520 , and the foldable display area  530  are integrally formed and display a screen together. The foldable display area  530  is in a curved state when the foldable display device  11  is in a folded state and is in a flat state when the foldable display device  11  is in an unfolded state. The first bottom shell  100  is disposed below the first display area  510 . The second bottom shell  200  is disposed below the second display area  520 . 
     The lifting mechanism comprises a support member  830 , a first support rod  811 , a second support rod  812 , a third support rod  813 , and a fourth support rod  814 . The support member  830  is disposed below the foldable display area  530 . The support member  830  may be a rigid plate. Top ends of the first support rod  811  and the third support rod  813  are rotatably connected to a first side  831  of the support member  830 , and top ends of the second support rod  812  and the fourth support rod  814  are rotatably connected to a second side  832  of the support member  830 . The second side  832  is opposite to the first side  831 . That is, the first support rod  811  and the second support rod  812  are disposed below a first side  531  of the foldable display area  530 . The third support rod  813  and the fourth support rod  814  are disposed below a second side  532  of the foldable display area  530 . The first support rod  811  intersects the second support rod  812 . The third support rod  813  intersects the fourth support rod  814 . 
     The transmission mechanism comprises a first bottom rod  821 , a second bottom rod  822 , a first rack  841 , a second rack  842 , a third rack  843 , a fourth rack  844 , a first gear  851 , a second gear  852 , a third gear  853 , and a fourth gear  854 . Both ends of the first bottom rod  821  are respectively connected to the bottom end of the first support rod  811  and the bottom end of the third support rod  813 . Both ends of the second bottom rod  822  are respectively connected to the bottom end of the second support rod  812  and the bottom end of the fourth support rod  814 . The second bottom rod  822  is parallel to the first bottom rod  821 . The first rack  841  is connected to one end of the first bottom rod  821 . The second rack  842  is connected to the other end of the first bottom rod  821 . The third rack  843  is connected to one end of the second bottom rod  822 . The fourth rack  844  is connected to the other end of the second bottom rod  822 . The first gear  851  is connected to an end of a side of the second bottom shell  200  facing the first bottom shell  100 . The first gear  851  is disposed on and meshes with the first rack  841 . The second gear  852  is connected to the other end of a side of the second bottom shell  200  facing the first bottom shell  100 . The second gear  852  is disposed on and meshes with the second rack  842 . The first gear  851  and the second gear  852  may be integrally formed with the second bottom shell  200 . The third gear  853  is connected to an end of a side of the first bottom shell  100  facing the second bottom shell  200 . The third gear  853  is disposed on the third rack  843  and meshes with the third rack  843  and the first gear  851 . The fourth gear  854  is connected to the other end of a side of the first bottom shell  100  facing the second bottom shell  200 . The fourth gear  854  is disposed on the fourth rack  844  and meshes with the fourth rack  844  and the second gear  852 . The third gear  853  and the fourth gear  854  may be integrally formed with the first bottom shell  100 . 
     During the unfolding process of the foldable display device  11 , the first gear  851  and the third gear  853  rotate synchronously to bring the first rack  841  and the third rack  843  approach each other, and the second gear  852  and the fourth gear  854  rotate synchronously to bring the second rack  842  and the fourth rack  844  approach each other so that the first bottom rod  821  and the second bottom rod  822  approach each other, the bottom end of the first support rod  811  and the bottom end of the second support rod  812  approach each other, the bottom end of the third support rod  813  and the bottom of the fourth support rod  814  approach each other, and the support member  830  is raised in parallel with respect to the first bottom shell  100  and the second bottom shell  200  to a position providing support for the foldable display area  530 . That is, the transmission mechanism can apply a moment to the first support rod  811 , the second support rod  812 , the third support rod  813 , and the fourth support rod  814  during a unfolding process of the foldable display device  11  so that the bottom end of the first support rod  811  approach the bottom end of the second support rod  812 , and the bottom end of the third support rod  813  approach the bottom of the fourth support rod  814 . Therefore, the support member  830  provides support for the foldable display area  530  when the foldable display device  11  is in an unfolded state. 
     During a folding process of the foldable display device  11 , the first gear  851  and the third gear  853  rotate synchronously to bring the first rack  841  and the third rack  843  away from each other, and the second gear  852  and the fourth gear  854  rotate synchronously to bring the second rack  842  and the fourth rack  844  away from each other, so that the first bottom rod  821  and the second bottom rod  822  away from each other, the bottom end of the first support rod  811  and the bottom end of the second support rod  812  away from each other, the bottom end of the third support rod  813  and the bottom of the fourth support rod  814  away from each other, and the support member  830  descends in parallel with respect to the first bottom shell  100  and the second bottom shell  200   
     During the processes of unfolding and folding the foldable display device  11 , the transmission mechanism can convert a relative rotation of the first gear  851  and the third gear  853  into a linear movement of the first rack  841  and the third rack  843 , and convert a relative rotation of the second gear  852  and the fourth gear  854  into a linear movement of the second rack  842  and the fourth rack  844 . 
     In the first embodiment, the foldable display device  11  may further comprise a gear cover  900 . The gear cover  900  comprises a cover plate  910 , two side plates  920 , and two sliding grooves  930 . The cover plate  910  covers the lifting mechanism. The two side plates  920  are respectively disposed on two opposite sides of the cover plate  910 . The first gear  851  and the third gear  853  are rotatably connected to one side plate  920 . The second gear  852  and the fourth gear  854  are rotatably connected to the other side plate  920 . Each of centers of the first gear  851 , the second gear  852 , the third gear  853 , and the fourth gear  854  may be provided with a first threaded hole  175 . The two side plates  920  may be provided with a plurality of second threaded holes  185  at positions corresponding to the first gear  851 , the second gear  852 , the third gear  853 , and the fourth gear  854 . A bolt  197  is passed through each first threaded hole  175  and its corresponding second threaded hole  185  and combined with a nut  198 . Thereby, the first gear  851  and the third gear  853  are rotatably connected to one of the side plates  920 , and the second gear  852  and the fourth gear  854  are rotatably connected to the other side plate  920 . The two sliding grooves  930  are respectively disposed on the cover plate  910  near the two side plates  920 . One of sliding grooves  930  is configured for the first rack  841  and the third rack  843  to slide linearly therein, and the other sliding groove  920  is configured for the second rack  842  and the fourth rack  844  to slide linearly therein. 
     In the first embodiment, the foldable display device  11  further comprises a first middle frame  300  and a second middle frame  400 . The first middle frame  300  is disposed between the first bottom shell  100  and the first display area  510 . The first middle frame  300  is configured to support the first display area  510  when the foldable display device  11  is in the unfolded state. The second middle frame  400  is disposed between the second bottom shell  200  and the second display area  520 . The second middle frame  400  is configured to support the second display area  520  when the foldable display device  11  is in the unfolded state. When the foldable display device  11  is in the unfolded state, the transmission mechanism raises the support member  830  to a position where it can support the entire display panel  500  together with the first middle frames  300  and the second middle frame  400 . 
     In the first embodiment, the foldable display device  11  further comprises a first front frame  600  and a second front frame  700 . The first front frame  600  is disposed on the first display area  510  and surrounding the first bottom shell  100 . The second front frame  700  disposed on the second display area  520  and surrounding the second bottom shell  200 . 
     Please refer to  FIG. 11  and  FIG. 12 . A foldable display device of a second embodiment of the present invention is different from the foldable display device  11  of the first embodiment of the present invention in that: (1) an intersection of the first support rod  811  and the second support rod  812  is provided with a hinge  10 , and an intersection of the third support rod  813  and the fourth support rod  814  is provided with another hinge  10 , and (2) each of portions of the support member  830  rotatably connected to the top ends of the first support rod  811 , the second support rod  812 , the third support rod  813 , and the fourth support rod  814  is provided with a chute  20 . 
     The foldable display device of the second embodiment of the present invention has the same transmission mechanism as the first embodiment of the present invention. During the unfolding process of the foldable display device  11 , the first gear  851  and the third gear  853  rotate synchronously to bring the first rack  841  and the third rack  843  approach each other via the corresponding chutes  20 , and the second gear  852  and the fourth gear  854  rotate synchronously to bring the second rack  842  and the fourth rack  844  approach each other via the corresponding chutes  20 , so that the first bottom rod  821  and the second bottom rod  822  approach each other, the top end of the first support rod  811  and the top end of the second support rod  812  approach each other via the corresponding chutes  20 , the top end of the third support rod  813  and the top of the fourth support rod  814  approach each other via the corresponding chutes  20 , and the support member  830  is raised in parallel with respect to the first bottom shell  100  and the second bottom shell  200  to a position providing support for the foldable display area  530 . During a folding process of the foldable display device  11 , the first gear  851  and the third gear  853  rotate synchronously to bring the first rack  841  and the third rack  843  away from each other, and the second gear  852  and the fourth gear  854  rotate synchronously to bring the second rack  842  and the fourth rack  844  away from each other, so that the first bottom rod  821  and the second bottom rod  822  away from each other, the top end of the first support rod  811  and the top end of the second support rod  812  away from each other via the corresponding chutes  20 , the top end of the third support rod  813  and the top of the fourth support rod  814  away from each other via the corresponding chutes  20 , and the support member  830  descends in parallel with respect to the first bottom shell  100  and the second bottom shell  200   
     According to the principle of leverage, a ratio of a distance from the top end of the first support rod to the adjacent hinge to a distance from the bottom end of the first support rod to the same hinge, a ratio of a distance from the top end of the second support rod to the adjacent hinge to a distance from the bottom end of the second support rod to the same hinge, a ratio of a distance from the top end of the third support rod to the adjacent hinge to a distance from the bottom end of the third support rod to the same hinge, and a ratio of a distance from the top end of the fourth support rod to the adjacent hinge to a distance from the bottom end of the fourth support rod to the same hinge are set to greater than 0 and less than or equal to 1. Thereby, lifting and lowering of the support  830  is more labor-saving. 
     Please refer to  FIG. 13  and  FIG. 14 . A foldable display device of a third embodiment of the present invention is different from the foldable display device  11  of the first embodiment of the present invention in that: (1) an intersection of the first support rod  811  and the second support rod  812  is provided with a hinge  10 , and an intersection of the third support rod  813  and the fourth support rod  814  is provided with another hinge  10 , (2) the support member  830  is a flexible plate made of a flexible material or a plurality of rigid strips connected together by a rotating shaft, and (3) in the transmission mechanism, the first gear  851  is disposed below and meshes with the first rack  841 , the second gear  852  is disposed below and meshes with the second rack  842 , the third gear  853  is disposed below the third rack  843  and meshes with the third rack  843  and the first gear  851 , and the fourth gear  854  is disposed below the fourth rack  844  and meshes with the fourth rack  844  and the second gear  852 . 
     During a unfolding process of the foldable display device, the first gear  851  and the third gear  853  rotate synchronously to bring the first rack  841  and the third rack  843  away from each other, and the second gear  852  and the fourth gear  854  rotate synchronously to bring the second rack  842  and the fourth rack  844  away from each other so that the first bottom rod  821  and the second bottom rod  822  away from each other, the top end of the first support rod  811  and the top end of the second support rod  812  away from each other, and the top end of the third support rod  813  and the top of the fourth support rod  814  away from each other. When the foldable display device is in an unfolded state, the support member  830  is in an unfolded state and provides support for the foldable display area  530 . 
     During a folding process of the foldable display device, the first gear  851  and the third gear  853  rotate synchronously to bring the first rack  841  and the third rack  843  approach each other, and the second gear  852  and the fourth gear  854  rotate synchronously to bring the second rack  842  and the fourth rack  844  approach each other so that the first bottom rod  821  and the second bottom rod  822  approach each other, the top end of the first support rod  811  and the top end of the second support rod  812  approach each other, and the top end of the third support rod  813  and the top of the fourth support rod  814  approach each other. When the foldable display device is in a folded state, the support plate  830  is bent and accommodated in a space defined by the first support rod  811 , the second support rod  812 , the third support rod  813 , and the fourth support rod  814  from their top ends to their adjacent intersections. Furthermore, the foldable display area  530  may be bent and accommodated in the bent support member  830 . 
     According to the principle of leverage, a ratio of a distance from the top end of the first support rod to the adjacent hinge to a distance from the bottom end of the first support rod to the same hinge, a ratio of a distance from the top end of the second support rod to the adjacent hinge to a distance from the bottom end of the second support rod to the same hinge, a ratio of a distance from the top end of the third support rod to the adjacent hinge to a distance from the bottom end of the third support rod to the same hinge, and a ratio of a distance from the top end of the fourth support rod to the adjacent hinge to a distance from the bottom end of the fourth support rod to the same hinge are set to greater than 0 and less than or equal to 1. Thereby, lifting and lowering of the support  830  is more labor-saving. 
     When a foldable display device of the present invention is in an unfolded state, a support member of a lifting mechanism provides support for a foldable display area by a transmission mechanism. This prevents the foldable display area from collapsing due to finger pressing, or wrinkling and peeling due to bending. In the above, the present application has been described in the above preferred embodiments, but the preferred embodiments are not intended to limit the scope of the present application, and those skilled in the art may make various modifications without departing from the scope of the present application. The scope of the present application is determined by claims.