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TECHNICAL FIELD 
     The present invention relates to a pivotable support shaft for connecting a display with a base member and supporting the display. 
     BACKGROUND ART 
     Displays, such as liquid crystal displays, are rotatably mounted on a base member by a pivotable support shaft. Support shaft assemblies available now generally have a fixed pivot range. i.e., they are able to pivot within a fixed range of pitch angle. However, it may be desired that the display have different postures in working condition and package and transporting condition. For example, in the working condition, the screen of the display may be pivotable between a pitch-up angle of about 20° and a pitch-down angle of about −20°, and in the package and transporting condition, the screen of the display may be pivoted down to a pitch-down angle of about −90° where the screen faces downwardly to reduce the package size and improve the transportation stability. This requires the displays having different pivot ranges which cannot be achieved by known support shaft assemblies. 
     SUMMARY OF INVENTION 
     An object of the present invention is to overcome the above shortage existed in the prior art by providing a pivotable support shaft for display which can be switched between a working condition and a package condition. 
     To achieve this object, the present invention provides a pivotable support shaft for display, comprising a main shaft, a first connecting seat, a retaining plate and a retaining pin, wherein the main shaft is to be fixed to a mounting base member of the display, the first connecting seat is to be attached to a back portion of the display, the first connecting seat is mounted on the main shaft in a manner that the first connecting seat is fixed in the axial direction of the main shaft and is able to rotate around the main shaft, the first connecting seat comprises a retaining surface, the retaining plate is mounted on the main shaft in a manner that it is restricted from rotating around the main shaft, the retaining plate comprises a first, a second and a third retaining edges, the retaining pin is mounted on the first connecting seat in a way of moving together with it, the retaining pin has a freedom-of-movement in the axial direction of the main shaft with a moving path delimitated by a first position and a second position, wherein in the first position, the retaining pin extends into a space between the first and second retaining edges, with the first and second retaining edges being in the rotating path of the retaining pin and the third retaining edge being outside of the rotating path of the retaining pin, and in the second position, the first and second retaining edges being outside of the rotating path of the retaining pin and the third retaining edge being in the rotating path of the retaining pin. 
     Preferably, a shifting lever is fixed to the retaining pin, an elastic member is disposed around the retaining pin in the axial direction of the main shaft, with the opposite ends of the elastic member bearing against the shifting lever and the first connecting seat respectively, to pushing the retaining pin towards the first position, and the retaining pin can be pushed by the shifting lever against the elastic urging force of the elastic member towards the second position. 
     Preferably, the first connecting seat comprises a first connecting base plate as well as a first main shaft supporting plate and a retaining pin supporting plate bent in the same direction from a surface of the first connecting base plate, the first main shaft supporting plate and the retaining pin supporting plate each comprises a through hole, the retaining pin is inserted through the two through holes in the axial direction of the main shaft so as to be supported by the first main shaft supporting plate and the retaining pin supporting plate, and the opposite ends of the elastic member bear against the retaining pin supporting plate and the shifting lever respectively. 
     Preferably, the first main shaft supporting plate and the retaining plate is disposed around the main shaft, a first fastener, washers as well as elastic shims for adjusting rotational damping force are also assembled around the main shaft, the first fastener, the first elastic shims, the first main shaft supporting plate, the washers and the retaining plate are disposed in this order, the first fastener is screwed on an end the main shaft, and the first main shaft supporting plate and the retaining plate are compressed on the main shaft in the axial direction of the main shaft by the first elastic shims. 
     Preferably, the washer comprises a hook portion, the retaining plate comprises a clamping hole, with the hook portion engaged into the clamping hole, the retaining plate comprises an anti-rotation hole, the main shaft comprises an anti-rotation shoulder, and the anti-rotation hole fits with the anti-rotation shoulder. 
     Preferably, the third retaining edge is formed as a retaining lug integrally extending from the outer periphery of the retaining plate in the axial direction of the main shaft towards the first connecting seat. 
     Preferably, the outer periphery of the retaining plate is formed with a recessed notch, with the first and second retaining edges being opposite end edges of the recessed notch. 
     Preferably, the main shaft comprises a left shaft section, a middle shaft section and a right shaft section which are integrally formed in this order, the first connecting seat is mounted to the left shaft section, the second connecting seat is mounted to the right shaft section, the second connecting seat is fixed in the axial direction of the main shaft and is rotatable around the main shaft, and the second connecting seat is to be fixed to the back portion of the display. 
     Preferably, the second connecting seat comprises a second connecting base plate and a second main shaft supporting plate bent from a surface of the second connecting base plate, the second main shaft supporting plate is disposed around the main shaft, a second fastener and second elastic shims for adjusting rotational damping force are also assembled around the main shaft, the second fastener is screwed on an end of the right shaft section, and the second main shaft supporting plate is compressed on the main shaft in the axial direction of the main shaft by the second elastic shims. 
     The present invention can thus obtain an advantage over the prior art. Specifically, when the retaining pin is in the first position, the pivotable support shaft for display is located in the working condition and is capable of pivoting up and down within a small pitch angle, and when the retaining pin is in the second position, the pivotable support shaft for display is located in the package condition by pitching down through a large pitch-down angle, thus the pivotable support shaft for display is able to be switched between the working condition and the package condition. 
    
    
     
       BRIEF INTRODUCTION TO THE DRAWINGS 
       The present invention will be described in details with reference to the drawings in which: 
         FIG. 1  is an exploded perspective view of an embodiment of the pivotable support shaft for display of the present invention. 
         FIG. 2  is a perspective view of the pivotable support shaft for display of the present invention. 
         FIG. 3  is a front view of the pivotable support shaft for display of the present invention in a working condition. 
         FIG. 4  is a schematic view showing the position restraining of the pivotable support shaft for display of the present invention in the working condition. 
         FIG. 5  is a front view of the pivotable support shaft for display of the present invention in a package condition. 
         FIG. 6  is a schematic view showing the position restraining of the pivotable support shaft for display of the present invention in the package condition. 
         FIG. 7  is a left side view of the pivotable support shaft for display of the present invention in the package condition. 
         FIG. 8  is a sectional view showing the position and connection relationship of a first connecting seat, a retaining pin, an elastic member and a shifting lever. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIGS. 1 to 8 , the pivotable support shaft for display according to an embodiment of the present invention is used to connect a display, such as a liquid crystal display, with a base member and to support the display, with the display being able to pivot relative to the base member. The pivotable support shaft for display mainly comprises a main shaft  1 , a first connecting seat  2 , a second connecting seat  3 , a retaining plate  4 , a shifting lever  5 , an elastic member  6  and a retaining pin  7 . 
     The main shaft  1  comprises a left shaft section  12 , a middle shaft section  11  and a right shaft section  13  which are integrally formed in this order along a common axis. The outer diameter of the middle shaft section  11  is larger than that of the left shaft section  12  and that of the right shaft section  13 , thus a step is formed between the middle shaft section  11  and each of the left and right shaft section  12  and  13 . The middle shaft section  11  is formed with a base member mounting surface  111  and a plurality of base member connecting holes  112  formed through the base member mounting surface  111 . When the base member mounting surface  111  is snugly attached to a fitting surface of the base member, a plurality of screws are inserted through the base member connecting holes  112  to connect the main shaft  1  with the base member. The left shaft section  12  is a shaft portion having a double-D shaped cross-section delimited by two outward-facing arc segments interposed between two parallel planes. At one end of the left shaft section  12  which joints to the middle shaft section  11 , there is provided with an anti-rotation shoulder  121  having a double-D shaped cross-section. Outer screw threads  122  are formed on the other end of the left shaft section  12 , and outer screw threads  131  are formed on the outer end of the right shaft section  13 . 
     The first connecting seat  2  comprises a first connecting base plate  21 , a first main shaft supporting plate  22  and a retaining pin supporting plate  23 . The first main shaft supporting plate  22  and the retaining pin supporting plate  23  are bent perpendicularly in the same direction from a surface of the first connecting base plate  21 . The first connecting base plate  21  is formed with a plurality of (shown as three) first screw through holes  211  for mounting the display. The first main shaft supporting plate  22  is formed with a first main shaft connecting hole  221  to be fit with the left shaft section  12  of the main shaft, and a clamping hole  223  juxtaposed to the connecting hole  221 . 
     The second connecting seat  3  comprises a second connecting base plate  31  and a second main shaft supporting plate  32  perpendicularly bent from a surface of the second connecting base plate  31 . The second connecting base plate  31  comprises a plurality of (shown as three) second screw through holes  311  for mounting the display. The second main shaft supporting plate  32  comprises a second main shaft connecting hole  321  to be fit with the right shaft section  13  of the main shaft, and a clamping hole  322  juxtaposed to the connecting hole  321 . 
     The retaining plate  4 , at its central portion, comprises an anti-rotation hole  41  formed therethrough along the axial direction of the main shaft  1  and having a double-D shaped cross-section. The anti-rotation hole  41  fits with the anti-rotation shoulder  121  of the left shaft section. The retaining plate  4 , on its outer periphery, comprises a recessed notch  42 . The recessed notch  42  comprises a first retaining edge  421  and a second retaining edge  422 . The retaining plate  4 , at its outer periphery, further comprises a protruded retaining lug  43 . The retaining lug  43  extends towards the first connecting seat  2  along the axial direction of the main shaft. The retaining plate  4  further comprises a clamping hole  44  juxtaposed to the anti-rotation hole  41 . 
     The retaining pin  7 , as shown in  FIG. 8 , is formed in a stepped shaft form comprising a large-diameter section  71 , an intermediate-diameter section  72  and a small-diameter section  73  in an order of decreasing diameters. The retaining pin supporting plate  23  of the first connecting seat  2  comprises a first retaining pin through hole  231 , and the first main shaft supporting plate  22  of the first connecting seat  2  comprises a second retaining pin through hole  222 , with the inner diameter of the first retaining pin through hole  231  fitting with the intermediate-diameter section  72  of the retaining pin  7 , and the inner diameter of the second retaining pin through hole  222  fitting with the small-diameter section  73  of the retaining pin  7 . The retaining pin  7  is supported in the axial direction of the main shaft  1  on the retaining pin supporting plate  23  and the first main shaft supporting plate  22 , with the large-diameter section  71  being located outside of and abutting against the retaining pin supporting plate  23  to prevent the retaining pin from being pulled out in a direction from the large-diameter section to the small-diameter section. The intermediate-diameter section  72  is inserted through the first retaining pin through hole  231 , and the small-diameter section  73  is inserted through second retaining pin through hole  222 . The small-diameter section  73  of the retaining pin is formed with a radial small receiving hole. By inserting the shifting lever  5  into the receiving hole, the shifting lever  5  and the retaining pin  7  are connected to be moved together. The intermediate-diameter section  72  of the retaining pin  7  is inserted through an elastic member  6 , the opposite ends of which bear against the shifting lever  5  and the retaining pin supporting plate  23  respectively. The elastic member  6  is in a compressed condition. The elastic member  6  may be composed by a known helical spring  6 . 
     The assembling of the pivotable support shaft for display will be described now. With reference to  1 , a friction-resistive washer  80 , the second connecting seat  3 , a further friction-resistive washer  80 , an anti-rotation plain washer  81 , four second elastic shims  82  and a further anti-rotation plain washer  81  are assembled onto the right shaft section  13  of the main shaft in sequence and are then are fastened by an anti-loose nut  83 . The two friction-resistive washers  80  clamp the second main shaft supporting plate  32  of the second connecting seat  3  therebetween. The two friction-resistive washers  80  each have a hook portion  801 . The hook portions  801  engage into the clamping hole  322  of the second main shaft supporting plate  32  from left and right sides respectively, to fix the friction-resistive washers  80  to the second main shaft supporting plate  32 , so that the friction-resistive washers  80  can be moved together with the second main shaft supporting plate  32 . Rotational friction from outside is taken by the two washers  80 . The two anti-rotation plain washers  81  are each formed with an inner hole  811  having a double-D shaped cross-section to fit with the right shaft section  13  having a corresponding double-D shaped cross-section, so that the four second elastic shims  82  and the anti-loose nut  83  are fastened to the main shaft  1  and to be moved together with it. The second elastic shims  82  may be known disc springs  82 . The disc springs  82  are divided into two groups with each group including two disc springs facing each other. The two groups are disposed side by side and are fastened from outside by the anti-loose nut  83 , so that the disc springs  82  are compressed. After assembled in this way, the second connecting seat  3  with the left and right friction-resistive washer  80  can be rotated around the main shaft  1 , and the second connecting seat  3  is fixed in the axial direction of the main shaft  1 . By adjusting the fastening level of the anti-loose nut  83 , the compression level of the disc springs  82  can be adjusted, and thus the damping force in rotation can be controlled in this way. On the other hand, onto the left shaft section  12  of the main shaft, the retaining plate  4  is first assembled. The anti-rotation hole  41  of the retaining plate  4  having a double-D shaped cross-section fits onto the anti-rotation shoulder  121  of the left shaft section  12  having a corresponding double-D shaped cross-section, so that relative rotation between the retaining plate  4  and the main shaft  1  is prevented. Then, a friction-resistive washer  84  is assembled onto the left shaft section  12 . The friction-resistive washer  84  has a hook portion  841  engaging into the clamping hole  44  of the retaining plate  4 . After that, the first connecting seat  2  and two friction-resistive washers  84  are assembled onto the left shaft section  12 , with the two friction-resistive washer  84  clamping the first main shaft supporting plate  22  of the first connecting seat from left and right sides respectively. The two friction-resistive washers  84  each have a hook portion  841  engaging into the clamping hole  223  of the first main shaft supporting plate  22 , so that the relative rotational friction between the first connecting seat  2  and the retaining plate  4  is taken by the friction-resistive washer  84 , so as to protect key members. Then, onto the left shaft section  12 , an anti-rotation plain washer  85 , four first elastic shims  86 , an anti-rotation plain washer  85  and an anti-loose nut  87  are assembled in sequence and are then are fastened by the anti-loose nut  87  with a suitable fastening force. Afterwards, the retaining pin  7  is inserted through the first retaining pin through hole  231  of the retaining pin supporting plate  23 , with the spring  6  assembled around the intermediate-diameter section  72  of the retaining pin  7 . Then, the retaining pin  7  is inserted through the second retaining pin through hole  222  of the first main shaft supporting plate  22 , and the shifting lever  5  is inserted into the radial receiving hole of the retaining pin  7  and is clamped therein. 
     When it needs to assemble the pivotable support shaft for display with the display and the base member, the main shaft  1  is fixed onto the base member. Then the first and second connecting base plates  21  and  31  of the first and second connecting seats  2  and  3  are attached to the back portion of the display, and screws are screwed through the screw through holes  211  and  311  of the first and second connecting seats  2  and  3  to fix the display to the first and second connecting seats  2  and  3 . Thus, the display and base member are connected by the pivotable support shaft. 
     The switching of the pivotable support shaft for display between different pivot ranges will now be described. 
     With reference to  FIGS. 3 and 4 , in a working condition, the pivot range of the display is designed as between a pitch-up angle of about 20° and a pitch-down angle of about −20°, wherein pivoting or rotating the display will cause the first and second connecting seats  2  and  3  rotate around the main shaft  1 . In the working condition, the small-diameter section  73  of the retaining pin  7  extends beyond the second retaining pin through hole  222  into a space between the first and second retaining edges  421  and  422  of retaining plate  4 . The spring  6  is always in the compressed condition, with its elastic urging force pushing against the shifting lever  5  and the retaining pin  7 , so that the retaining pin  7  remains a stable position. When the display pivot upwardly to a pitch-up angle of about 20°, the small-diameter section  73  of the retaining pin  7  contacts the first retaining edge  421  of the retaining plate  4  and thus stops the pivoting of the display. When the display pivot downwardly to a pitch-down angle of about −20°, the small-diameter section  73  of the retaining pin  7  contacts the second retaining edge  422  of the retaining plate  4  and thus stops the pivoting of the display. 
     In a package and transporting condition, the screen of the display is preferred to pivot downwardly to a pitch-down angle of about −90°, which needs to change the pivot range of the pivotable support shaft. To this end, with reference to  FIGS. 5 to 7 , the shifting lever  5  is pushed outwardly along a direction shown by the arrow of  FIG. 5  to a position shown in  FIG. 5 . Now the small-diameter section  73  of the retaining pin  7 , in the axial direction of the main shaft, falls outside of an end surface  40  of the retaining plate  4 , where the small-diameter section  73  is free from being retained by the second retaining edge  422  of the retaining plate  4 . In this condition, the first and second connecting seats are able to pivot downwardly beyond the pitch-down angle of about −20°. The display moves downwardly together with the connecting seats. Now, if the shifting lever  5  is released, the shifting lever  5  and the retaining pin  7  will return inwardly under the elastic urging force of the spring  6 . In this condition, the small-diameter section  73  of the retaining pin  7  has already disengaged from the recessed notch  42  of the retaining plate  4 , so the small-diameter section  73  can only abut against the end surface  40  of the retaining plate  4 . That is to say, the small-diameter section  73  of the retaining pin  7  does not have any position retaining effect now. Then, the first and second connecting seat  2  and  3  pivot continuously downwardly with the display, until the display pivots downwardly to the pitch-down angle of about −90°, where a retaining surface  224  of the first connecting seat  2  contacts the retaining lug  43  of the retaining plate  4 , so that the display cannot pivot any further. 
     When the package is opened and it needs to set the display back to the working condition, the only action necessary to take is to force the display to pivot upwardly. When the display pivots upwardly beyond the pitch-down angle of about −20°, the retaining pin  7  will be pushed into the recessed notch  42  of the retaining plate  4  under the elastic urging force of the spring  6 . Thus the pivot rage of the working condition is restored. 
     The present invention is described with reference to its preferred embodiments which are not intended to restrict the scope of the present invention. A skilled in the art will readily recognize that modifications and changes can be made to these embodiments without departing from the spirit of the present invention, and accordingly all these modifications and changes may be regarded as falling within the scope of the present invention.

Summary:
A pivotable support shaft for connecting a display with a base member and supporting the display is disclosed. The support is designed to enable the display to have different postures in working condition and package and transporting condition. For example, in the working condition, the screen of the display may be pivotable between a pitch-up angle of about 20° and a pitch-down angle of about −20°, and in the package and transporting condition, the screen of the display may be pivoted down to a pitch-down angle of about −90° where the screen faces downwardly to reduce the package size and improve the transportation stability.