A hinge assembly ( 200 ) for joining a cover section ( 110 ) to a body section ( 120 ) of a foldable electronic device ( 100 ) includes a main shaft ( 10 ), a rotating member ( 20 ), a sliding member ( 30 ), and a spring ( 40 ). The main shaft has a fixing portion ( 12 ) at one end, a deformed shaft portion ( 14 ) at its central section, and a distal shaft portion ( 16 ) at the other end. The rotating member receives the distal shaft portion, and the rotating member includes an engaging portion ( 24 ). The sliding member engages with the deformed shaft portion. The sliding member has a deformed hole ( 34 ), engaging with the engaging portion of the rotating member. The spring surrounds the main shaft and elastically biases between the sliding member and the fixing portion. The hinge assembly is modularized, easy to install, and low in cost.

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to hinge assemblies and, particularly, to a hinge assembly for foldable electronic devices such as portable telephones, portable computers, PDA (Portable Digital Assistant) and so on. 
     2. Discussion of the Related Art 
     At present, perhaps the most popular portable electronic device in the marketplace is the foldable cellular telephone, which generally includes a cover section and a body section. The cover section and the body section are rotatably interconnected through a hinge assembly, for switching the telephone between an in-use position and a closed position. 
     One kind of hinge assembly employs a compression coil spring and a cam to make the cover section open up from the body section and be held in an open position. An example of such a kind of hinge assembly is represented in  FIG. 8  (Prior Art). That hinge assembly is used in a foldable mobile phone  70 . The foldable mobile phone  70  includes a main housing  72  and a cover  74 . The hinge assembly includes two cams  60 ,  62 , a spring  64 , and a pair of posts  76  contained in the main housing  72 . The cover  74  has a channel  742  defined at an end thereof. The cam  62 , the spring  64 , and the cam  60  are fixed in the channel  742 , in that order. The cams  60 ,  62  protrude out from the channel  742  and engage with the posts  76 . When the cover  74  is rotated, the cams  60 ,  62  rotate along with the cover  74 , until stopping the cover  74  in a position where it maintains an angle of 180° relative to the main housing  72 . 
     However, the hinge assembly includes a variety of individual pieces that must be installed within the foldable mobile phone when the foldable mobile phone is assembled. This does not meet the growing trend for foldable mobile phone manufacturers to use integrated one-piece hinge assemblies that can be quickly and easily press-fitted into foldable mobile phone sub-assemblies during manufacturing. Manufacturing costs associated with non-integrated hinge assemblies are higher than those associated with one-piece hinge assemblies. 
     Accordingly, what is needed is a hinge assembly for devices such as mobile phones, in which the hinge assembly modularized, easy to be installed into foldable mobile phones, and low in cost. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present hinge assembly includes a main shaft, a rotating member, a sliding member, and a spring. The main shaft has a fixing portion at one end, a deformed shaft portion at its central section, and a distal shaft portion at the other end. The rotating member receives the distal shaft portion of the main shaft, and the rotating member includes an engaging portion. The sliding member operatively mates with the deformed shaft of the main shaft. The sliding member has a deformed hole, matingly engaging with the engaging portion of the rotating member. The spring surrounds the main shaft and elastically biases against the sliding member and the fixing portion of the main shaft. 
     Other objects, advantages and novel features of the present hinge assembly will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the hinge assembly can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present hinge assembly. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is an isometric view of an embodiment of the present hinge assembly, as used in a mobile phone; 
         FIG. 2  is an exploded, isometric view of the embodiment of the hinge assembly shown in  FIG. 1 ; 
         FIG. 3  is similar to  FIG. 2 , but viewed from another aspect; 
         FIG. 4  is a side sectional view of a rotational member of the hinge assembly in  FIG. 2 ; 
         FIG. 5  is a side sectional view of a sliding member of the hinge assembly in  FIG. 2 ; 
         FIG. 6  is an isometric view showing the hinge assembly in a position corresponding to an open state of the mobile phone; 
         FIG. 7  is similar to  FIG. 6 , but showing the hinge assembly in a position corresponding to a closed state of the mobile phone; and 
         FIG. 8  is an exploded, isometric view of a conventional hinge assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail,  FIG. 1  shows that a hinge assembly  200 , applied to a portable electronic device  100  such as a flip type mobile phone, for pivotably coupling a cover section  110  and a body section  120  together. It is to be understood, however, that the hinge assembly  200  could be advantageously used in other environments (e.g., cabinet doors). As such, although proving particularly advantageous when used in foldable electronic devices, the hinge assembly  200  should not be considered limited in scope solely to an intended use environment of foldable electronic devices. 
     Referring to  FIGS. 2 and 3 , the hinge assembly  200  includes a main shaft  10 , a rotating member  20 , a sliding member  30 , a spring  40 , and a locking member  50 . The spring  40 , the sliding member  30 , and the rotating member  20  are placed, in that order, to surround the main shaft  10 . The locking member  50  is locked at one end of the main shaft  10 , adjacent the rotating member  20 . Accordingly, all of the elements are installed together. 
     The main shaft  10  includes a fixing portion  12 , a flat-sided shaft portion  14  (e.g. having two-flat sides in the illustrated embodiment) and a distal shaft portion  16 , either connecting or integral with each other. The fixing portion  12  is substantially a cuboid (i.e., a rectangular parallelepiped, likely (although not necessarily) having a pair of opposing square faces), formed at an end of the flat-sided shaft portion  14 . The fixing portion  12  is configured for engaging with the body section  120 . The flat-sided shaft portion  14  is formed/positioned at an intermediate location between the fixing portion  12  and the distal shaft portion  16 . The flat-sided shaft portion  14  has two opposed flat surfaces  142  defined thereon. The distal shaft portion  16  is formed at an opposite end of the flat-sided portion  14  and has a loop groove  162  defined at a distal end thereof. 
     Also referring to  FIG. 4 , the rotating member  20  includes a latching portion  22  and an engaging portion  24  connected with the latching portion  22 . The latching portion  22  is substantially a cylinder or disk. Two symmetrically opposite protrusions  222  are formed at (i.e., on) a peripheral wall of the latching portion  22 , each protrusion  222  being configured for engaging with the cover section  110  in a manner that allows the given protrusion  222  to only slide relative to the cover section  110 . While two such protrusions  222  are shown, it is to be understood any number of protrusions  222  could be employed and still be within the scope of the hinge assembly  200 . The engaging portion  24  is substantially a twisted/torsional cylinder, as can be seen from FIGS.  2  and  4 - 7 , with two opposite end surfaces  242 ,  244 . The two opposite end surfaces  242  and  244  are the congruent, parallel ellipses, each perpendicular to an axis of the rotating member  20  (i.e., the opposite end surfaces  242  and  244  are “twisted” 90° relative to one another). A long axis of the end surface  242  is parallel with a short axis of the opposite end surface  244 . A smooth exterior twisted surface is formed between the two end surfaces  242 ,  244 . The rotating member  20  has a circular through hole  26  defined therein. The circular through hole  26  receives therein the distal shaft portion  16  of the main shaft  10 , thereby allowing the rotating member  20  to rotate relative to the main shaft  10 . 
     Also referring to  FIG. 5 , the sliding member  30  is substantially a cylinder, with an engaging hole  32  and a elliptical hole  34 . The engaging hole  32  and the elliptical hole  34  are respectively defined in two sides of the sliding member  30  and are in communication with each other. The engaging hole  32  has two opposing arcuate faces and two opposing flat faces (faces not labeled). As such, the engaging hole  32  is configured for engagingly receiving the flat-sided shaft portion  14  of the main shaft  10 , so as to only slide relative to the flat-sided portion  14 . The elliptical hole  34  is generally elliptical, similar to the end face  242  of the engaging portion  24 , and is thus configured for engaging with the engaging portion  24  of the rotating member  20 . 
     The spring  40  is substantially a cylinder (i.e., occupying a cylindrical volume). The spring  40  is placed around to the main shaft  10 , with one end of the spring  40  resisting/biasing the sliding member  30 , the opposite end of the spring  40  resisting the fixing portion  12  of the main shaft  10 . In this manner, the spring  40  is effectively configured for promoting/maintaining the operative contact (i.e., engagement) between the sliding member  30  and the rotating member  20  by effectively elastically biasing such members  20 ,  30  toward one another. Such contact between members  20 ,  30  could instead potentially be promoted, e.g., by relocating (embodiment not shown) the spring  40  to a location between the rotating member  20  and the locking member  50  or by adding an additional spring (not shown) between the members  20 ,  50 . The spring force applied to the members  20 ,  30  should be sufficient to ensure contact therebetween but should not be so large as to prevent slidable movement relative to one another. 
     The locking member  50  has a substantially C configuration. The locking member  50  locks in the groove  16  of the main shaft  10  so as to thereby prevent the sliding member  30  and rotating member  20  from coming off the main shaft  10  during operation. 
     In assembly, referring to  FIGS. 6 and 7 , the distal shaft portion  16  of the main shaft  10  is inserted through the spring  40 , the sliding member  30 , and the rotating member  20 . The locking member  50  is locked into the loop groove  162  of the main shaft  10 . Once the individual hinge components are assembled as described above, the hinge assembly  200  provides a self-contained component that can be sold as an off-the-shelf component or directly incorporated into a mobile phone or other device during manufacture. If incorporated into the mobile phone during manufacture, the protrusions  222  engage in a cavity (not shown) of the cover section  110  of the mobile phone  100 , and the fixing portion  12  of the main shaft  10  engages in the body section  120  of the mobile phone  100 . When the cover section  110  of the mobile phone  100  is in a fully closed position, the engaging portion  24  is totally received in the deformed hole  34  of the sliding member  30 , and the hinge assembly  200  is in a steady state. 
     In use, when the cover section  110  of the mobile phone  100  is moved from the closed position to the open position by force, the cover section  110  causes the rotating member  20  to rotate relative to the body section  120 . The rotating member  20  further forces the sliding member  30  to rotate. However, the sliding member  30  is limited in its movement by the interconnection of the engaging hole  32  thereof with the flat-sided shaft  14  of the main shaft  10 . Thus, the sliding member  30  can only slide relative to the flat-sided shaft  14  of the main shaft  10 . Accordingly, when the rotating member  20  rotates, the sliding member  30  slides towards to the spring  40 . The spring  40  is thereby compressed. Once the rotating member  20  rotates 90 degrees, the hinge assembly  200  is at a critical state. The sliding member  30  passes over the critical state when a continued force is applied. Then, alter the force is stopped, the sliding member  30  adversely slides relative to the rotating member  20  due to the force of the spring  40 . The sliding member  30  pushes the rotating member  20 , inducing the rotation of the rotating member  20  until the sliding member  30  is at its next steady state. The cover section  110  is thus opened automatically to a fully open position under the decompression force of the spring  40 . Accordingly, the cover section  110  is moved 180 degrees relative to the body section  120 . Preferably, the structure of the cover section  110  and the body section  120  are adapted to control the degree of rotation of the hinge assembly  200 , such that the sliding member  30  can be held in one or more particular locations between the engaging portion  24  and the elliptical hole  34 . 
     When the cover section  110  of the mobile phone  100  is closed, the cover section  110  causes the rotating member  20  to rotate relative to the body section  120 . The sliding member  30  slides along the flat-sided shaft portion  14 . After the rotating member  20  rotates to the critical position, the sliding member  20  continues to rotate under the role of the spring  40  and the elliptical hole  34  of the sliding member  30  until the sliding member  30  tightly abuts the rotating member  20  at a stable state. Accordingly, the cover section  110  becomes closed relative to the body section  120 . 
     As described above, the present invention provides a hinge assembly  200  for use with any various portable devices, beyond the mobile phone illustrated, and/or with other devices needing a hinge assembly that selectably facilitates the achievement of fully open and fully closed positions. 
     It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.