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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to hinge assemblies used in electronic devices, and particularly to a hinge assembly for hinging a cover and a housing of a foldable electronic device together. The instant invention relates to a contemporarily filed application titled “HINGE FOR A PORTABLE ELECTRONIC DEVICE” and having the same assignee with the instant application. 
     2. Prior Art 
     Portable electronic devices, such as cellular phones and PDAs (personal digital assistants), are becoming ever more popular with the development of wireless communication technology and data processing technology. 
     For example, a foldable cellular phone commonly has two housings joined by some type of hinge that allows the housings to fold upon one another. Some foldable phones have most of the electronics provided in one of the housings, called the body. The other housing, called the cover, normally contains fewer electronic components than the body. Other foldable phones have essentially all the electronics provided in the body, with the cover serving only to cover and protect the keypad and the display of the phone. 
     U.S. Pat. No. 5,628,089, issued to Wilcox et al and entitled “Radiotelephone Having a Self Contained Hinge,” discloses a hinge for use in a miniaturized radiotelephone. This hinge is represented in  FIG. 6 . The hinge  20  comprises a spring  22 , a cam  23  and a follower  24  assembled into a cylindrically hollow can  21  via an open end thereof, and held in assemblage by a cap  25  coupled to the can  21  over the open end. The hinge  20  can be attached in a cavity of a cover and a cavity of a body of the radiotelephone. 
     This kind of self contained hinge is desired by some cellular phone manufacturers because it can be purchased as a separate unit, thereby eliminating the steps associated with assembling such hinge during manufacturing. However, a foldable cellular phone with such hinge can be opened automatically only after the cover has first been turned about the body by a user. It is not easy for the user to open the cellular phone with only one hand, for example when the user is driving a car or is otherwise occupied. Furthermore, the cover is prone to open quickly and jar against the body. After much use, the body and the cover are liable become worn out and not operate properly. 
     Thus, a need exists for a convenient and highly reliable hinge assembly which is suitable for use in a foldable electronic device, and which overcomes the above-described problems. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a hinge assembly for a foldable cellular phone, the hinge assembly being highly reliable and operable with a simple key or button. 
     Another object of the present invention is to provide a cover of a foldable electronic device, the cover having high reliability and being openable with a simple key or button. 
     To accomplish the above-mentioned objects, the present invention provides a hinge assembly for joining a body and a cover of a foldable mobile phone. The hinge assembly includes an inner housing, a key, a pressure spring, a can, a slider, a damper, an outer housing, a fastener, an orientation pin, and a torsion-bar spring. The can includes an acceptor that defines an axial slot in a peripheral wall thereof, and a protrusion having a stepped hole in a middle thereof. The slider has an adjoining block received in the stepped hole. One end of the torsion-bar spring is secured onto the fastener, and the other end of the torsion-bar spring is received in the slot of the can. The damper is disposed between the inner housing and the outer housing. A user presses the key to slidably remove the block of the slider from the stepped hole of the can, whereupon the torsion-bar spring can rotationally drive the slider and the fastener, with the outer housing turning in unison therewith. Thus the cover is opened. 
     The hinge assembly of the invention enables a foldable cellular phone to be opened by pressing a single key. Users can operate the phone more conveniently without having to use both hands. The damper is disposed between the outer housing and the inner housing of the hinge assembly. This can minimize any jarring of the cover that might otherwise occur, and minimizes inner abrasion of the hinge assembly. 
     Other objects, advantages and novel features of the invention will be drawn from the following detailed description with reference to the attached drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded, isometric view of a hinge assembly for a cellular phone in accordance with the present invention; 
         FIG. 2  is similar to  FIG. 1 , but viewed from another aspect; 
         FIG. 3  is a partly assembled, cut-away view of the hinge assembly of  FIG. 1 , but viewed from another aspect; 
         FIG. 4  is an enlarged, assembled, cut-away view of the hinge assembly of  FIG. 1 , but viewed from another aspect; 
         FIG. 5A  is a cross sectional view of the hinge assembly of  FIG. 4  taken along line V—V thereof, but showing a pressing portion of the hinge assembly depressed, and the hinge assembly in a position corresponding to the cellular phone being in an open state; 
         FIG. 5B  is a cross sectional view of the hinge assembly of  FIG. 4  taken along line V—V thereof, showing the pressing portion in a normal position, and the hinge assembly in a position corresponding to the cellular phone being in a closed state; and 
         FIG. 6  is an exploded, isometric view of a conventional hinge. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary embodiment of a hinge assembly in accordance with the present invention is shown in  FIGS. 1 and 2 . The hinge assembly  10  includes an inner housing  100 , a key  110 , a pressure spring  120 , a can  130 , a slider  140 , a damper  150 , an outer housing  160 , a fastener  170 , an orientation pin  180 , and a torsion-bar spring  190 . 
     The inner housing  100  includes a head  101  and a neck  102 , both of which are cylindrical and share a same axis. The head  101  is attached in a body of a cellular phone. A square setting hole  101   a  is defined in a middle of the head  101 . The setting hole  101   a  is a through hole, and is for engagingly receiving the key  110 . An inside of the neck  102  defines an accepting space  102   a , which can accept the key  110 , the pressure spring  120  and the can  130  in turn. 
     The key  110  is a step-like column which includes a pressing portion  111 , a cylindrical portion  112 , a step  114  and a driving peg  116 . The pressing portion  111  is generally cubical, and is shaped to be fittingly received in the setting hole  101   a.    
     The pressure spring  120  is helical. One end of the pressure spring  120  surrounds the step  114  and the driving peg  116  and abuts against the cylindrical portion  112  of the key  110 . An opposite end of the pressure spring  120  engages with the can  130 . 
     The can  130  includes an acceptor  132  and a protrusion  131 , both of which are cylindrical and share a same axis. The protrusion  131  defines a stepped hole in a middle thereof, the stepped hole comprising a first chamber  131   a  and a second chamber  131   b  (shown in  FIG. 3 ). The two chambers  131   a ,  131   b  share a same axis, and a radius of the first chamber  131   a  is greater than that of the second chamber  131   b . The first chamber  131   a  is shaped to fittingly receive the step  114  of the key  110 . The second chamber  131   b  is shaped to movably receive the driving peg  116  of the key  110 . The driving peg  116  can slide along the axis of the second chamber  131   b . A cavity  132   a  is defined inside the acceptor  132 , and an axial slot  132   b  is defined in a peripheral wall of the acceptor  132 . An open end of the axial slot  132   b  runs through the peripheral wall of the acceptor  132 , while an opposite closed end of the axial slot  132   b  does not. That is, the closed end of the axial slot  132   b  is only defined in an outside portion of the peripheral wall. An external radius of the acceptor  132  is slightly less than a radius of the accepting space  102   a  of the neck  102  of the inner housing  100 . 
     The slider  140  includes a cylindrical main body (not labeled) and an adjoining block  141 . The block  141  has a rectangular cross section, and is shaped to be fittingly received in the second chamber  131   b  of the protrusion  131 . The main body defines a generally rectangular hole  142  therein. When the driving peg  116  drives the block  141 , the slider  140  is pushed to axially slide in the cavity  132   a  of the can  130 . 
     The damper  150  is made from glue-like material that cannot become hardened, or is dampening oil. The damper  150  is disposed between the inner housing  100  and the outer housing  160 , to increase friction when the two housings  100 ,  160  move relative to each other. This can to some degree decrease the speed of rotation when a cover of the cellular phone rotates relative to a body thereof. 
     The outer housing  160  is a hollow cylinder connectable with the cover of the cellular phone. The outer housing  160  includes two orientation holes  161 , two cutouts  162 , and two parallel ribs  164  that connect the outer housing  160  and the cover. The orientation holes  161  are symmetrically defined in a peripheral wall of the outer housing  160 . The cutouts  162  are symmetrically defined in one end of the outer housing  160 . An internal radius of the outer housing  160  is slightly greater than an external radius of the inner housing  100 . 
     The fastener  170  is generally a hollow cylinder with one closed end. The fastener  170  includes a pair of orientation arms  171 , an axial pole  172 , and two limiting holes  174 . The orientation arms  171  are symmetrically opposite each other, and radially extend from the closed end of the fastener  170 . The orientation arms  171  can be coupled in the cutouts  162  of the outer housing  160 . The axial pole  172  extends from an inside of the closed end through a middle of the fastener  170 , and protrudes out from an opposite open end of the fastener  170 . The axial pole  172  is shaped to be fittingly received in the rectangular hole  142  of the slider  140 . The limiting holes  174  are defined symmetrically in a peripheral wall of the fastener  170 . 
     The orientation pin  180  is for extending through the orientation holes  161  and the limiting holes  174  in order to secure the fastener  170  in the outer housing  160 . The orientation pin  180  can alternatively be replaced by other suitable securing means such as pegs or dowels. 
     The torsion-bar spring  190  is generally helical, and has a first end  191  and an opposite second end  192 . The first end  191  is generally rectangular, so that it can be fixed around the axial pole  172  inside the fastener  170 . The first end  191  is thus secured with the fastener  170 . The second end  192  is coupled in the axial slot  132   b  of the can  130 , such that it can axially slide in the axial slot  132   b.    
     As shown in  FIG. 3 , when the hinge assembly  10  is assembled, if the damper  150  is solid, the damper  150  is attached to an internal surface of the outer housing  160 . The key  110  and then the pressure spring  120  are inserted into the accepting space  102   a  of the inner housing  100 . The pressing portion  111  protrudes out from the setting hole  101   a  of the head  101 . One end of the pressure spring  120  is received around the step  114  and the driving peg  116  of the key  110 , and abuts against the cylindrical portion  112 . The first end  191  of the torsion-bar spring  190  is secured around the axial pole  172  of the fastener  170 . The slider  140  and the fastener  170  with the torsion-bar spring  190  are received in turn into the cavity  132   a  of the can  130 . The torsion-bar spring  190  is simultaneously turned so that the second end  192  is received in the axial slot  132   b  of the can  130 . The assembled can  130  is disposed inside the inner housing  100 . The other end of the pressure spring  120  is placed around the protrusion  131  of the can  130 , and abuts against an outer stepped surface of the acceptor  132 . The driving peg  116  of the key  110  extends into the second chamber  131   b  of the protrusion  131 , and pushes the block  141  of the slider  140  to axially slide in the cavity  132   a  of the can  130 . The orientation pin  180  is threaded through the orientation holes  161  and the limiting holes  174  to attach the outer housing  160  and the fastener  170  together. Thus assembly of the hinge assembly  10  is achieved. 
     If the damper  150  is dampening oil, after the inner housing  11  accommodates the key  110 , the pressure spring  120 , the can  130  and the slider  140 , the exterior surface of the neck  102  of the inner housing  110  is coated with the damper oil. Then the outer housing  160  is received over the neck  102 . The orientation pin  180  is threaded through the orientation holes  161  and the limiting holes  174  to achieve the assembled hinge assembly  10 . 
     As shown in  FIGS. 4 and 5B , when the cover of the cellular phone is in a closed state, the driving peg  116  of the key  110  abuts against the block  141  of the slider  140 . The block  141  is in the second chamber  131   b  of the can  130 . The second end  192  of the torsion-bar spring  190  is in the axial slot  132   b  of the can  130 . 
     Referring also to  FIG. 5A , when a user presses on the pressing portion  111 , this forces the key  110  to move axially inwardly. The cylindrical portion  112  compresses the pressure spring  120 , and the driving peg  116  drives the block  141  axially inside the cavity  132   a  until the step  114  abuts against an inner stepped surface of the acceptor  132  where the first chamber  131   a  adjoins the second chamber  131   b . The torsion-bar spring  190  is compressed by the slider  140 , and drives the axial pole  172  of the fastener  170  to rotate. The fastener  170  drives the slider  140  and the outer housing  160  to rotate in unison, which makes the cover of the cellular phone rotate from the closed state to an open state. Simultaneously, the user releases the pressure spring  120 , which decompresses and pushes the key  110  back to its original position. When the cover is in the open state, an angle between the cover and the body of the cellular phone is approximately 180 degrees. The torsion-bar spring  190  drives the outer housing  160  to rotate until stopping means provided on the cover and the body of the cellular phone stop the cover in the open state. As mentioned previously, the cross section of the block  141  is rectangular, so that it can no longer enter the second chamber  131   b  of the protrusion  131 . Because the damper  150  provides friction between the inner housing  100  and the outer housing  160 , the rotation of the cover is slowed down. The slow opening of the cover minimizes any jarring of the cover that might otherwise occur, and minimizes inner abrasion of the hinge assembly  10 . 
     When the cover of the cellular phone is moved from the open state to the closed state, the slider  140  rotates in unison with the fastener  170  and the outer housing  160 . When the cover reaches the closed state, the block  141  of the slider  140  is aligned with the second chamber  131   b  of the protrusion  131 , and the torsion-bar spring  190  decompresses to drive the block  141  into the second chamber  131   b . A peripheral step of the slider  140  where the block  141  adjoins the main body of the slider  140  abuts against an inner step of the can  130  where the second chamber  131   b  adjoins the cavity  132   a . The slider  140  is thus stopped in its original position. The inner housing  100  and the outer housing  160  are back in their original positions, ready for the cover of the cellular phone to be opened again. 
     It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Summary:
A hinge assembly ( 10 ) for joining a body and a cover of a mobile phone includes an inner housing ( 100 ), a key ( 110 ), a pressure spring ( 120 ), a can ( 130 ), a slider ( 140 ), a damper ( 150 ), an outer housing ( 160 ), a fastener ( 170 ), and a torsion-bar spring ( 190 ). The can includes an acceptor ( 132 ) defining an axial slot ( 132   b ) in a peripheral wall thereof, and a protrusion ( 131 ) having a stepped hole. The slider has an adjoining block ( 141 ) received in the stepped hole. One end of the torsion-bar spring is secured onto the fastener, and the other end of the torsion-bar spring is received in the slot. A user presses the key to slidably remove the slider from the stepped hole of the can, whereupon the torsion-bar spring can rotationally drive the slider and the fastener, with the outer housing turning in unison therewith. Thus the cover is opened.