Patent Publication Number: US-2011072618-A1

Title: Hinge device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a hinge device, more particularly to a hinge device including a torque-adjustable torsion spring. 
     2. Description of the Related Art 
       FIG. 1  illustrates a conventional hinge device that includes a first leaf  11  mounted to a door panel (not shown) and provided with a first knuckle  111 , a second leaf  12  mounted to a door frame (not shown) and provided with a second knuckle  121  coupled to the first knuckle  111  through a pivot pin  14 , a washer  13  disposed between the first and second knuckles  111 ,  121  for facilitating the rotation of the first knuckle  111  relative to the second knuckle  121 , a cylindrical part  17  disposed in the second knuckle  121 , and a torsion spring  16  disposed in the second knuckle  121  and having one end connected to a rod  141  of the pivot pin  14  and the other end connected to the cylindrical part  17 . The pivot pin  14  is locked in the first knuckle  111  by two lock bolts  15  (only one is shown). The cylindrical part  17  is formed with a plurality of fastening holes  172 , and the second knuckle  121  is formed with a circumferentially extended slide groove  122  that is registered with some of the fastening holes  172 . A screw  18  is extended through the slide groove  122  and engages threadedly a selected one of the fastening holes  172 . 
     During the door-opening process, the first leaf  11  is pivoted relative to the second leaf  12 , such that the first knuckle  111  is driven to rotate relative to the second knuckle  121 , thereby twisting the torsion spring  16 . Afterward, a restoring force of the torsion spring  16  automatically drives the first knuckle  111  to rotate reversely relative to the second knuckle  121  to thereby result in an automatic reverse pivoting movement of the first leaf  11  relative to the second leaf  12 . Moreover, before the door-opening process, torque of the torsion spring  16  can be adjusted by removing the screw  18  from an initial fastening hole  172 , and engaging the screw  18  to another fastening hole  172 . 
     However, since the screw  18  slides along the slide groove  122  as the cylindrical part  17  rotates during the abovementioned torque-adjusting process, the torque of the torsion spring  16  can only be adjusted in a limited extent depending upon the length of the slide groove  122 . Moreover, if the door panel is relatively heavy, it will exert a relatively large pressure to the torsion spring  16  to thereby result in damage to the torsion spring  16  after long-term use. Furthermore, the relatively heavy door panel will also result in a relatively large friction between the washer  13  and the first and second knuckles  111 ,  121 , thereby hindering the rotation of the first knuckle  111  relative to the second knuckle  121 . 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the present invention is to provide a hinge device that can overcome at least one of the aforesaid drawbacks associated with the prior art. 
     According to this invention, a hinge device comprises a hinge unit, a torque-providing unit; and a torque-adjusting unit. The hinge unit includes a first leaf, a second leaf, and a knuckle unit that includes first and second knuckles provided respectively to the first and second leaves and coupled pivotally to each other such that the first leaf is rotatable relative to the second leaf. The first and second knuckles define cooperatively a channel unit that extends along an axis. The torque-providing unit includes a torsion spring that is disposed in the channel unit, and that has a first end secured to the second knuckle and a second end opposite to the first end. The torque-adjusting unit includes a cam mechanism that includes a cam coupled co-rotatably to the first knuckle, and a cam follower disposed rotatably in the first knuckle and coupled co-rotatably to the second end of the torsion spring of the torque-providing unit. The first knuckle and the cam are rotatable in a first rotational direction relative to the second knuckle as a result of application of a force to the first leaf so as to drive the cam to engage the cam follower and to drive the cam follower to rotate in the first rotational direction, thereby twisting the torsion spring. When the force is released, the cam follower is driven by a restoring force of the torsion spring to rotate in a second rotational direction opposite to the first rotational direction so as to drive the cam to rotate in the second rotational direction, thereby driving the first knuckle to rotate in the second rotational direction relative to the second knuckle. The cam follower is operable to rotate in the first rotational direction so as to twist the torsion spring, thereby adjusting the torque of the torsion spring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of the invention, with reference to the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view of a conventional hinge device; 
         FIG. 2  is an exploded perspective view of a first preferred embodiment of a hinge device according to this invention; 
         FIG. 3  is an assembled top view of the first preferred embodiment; 
         FIG. 4  is a sectional view of the first preferred embodiment; 
         FIG. 5  is another sectional view of the first preferred embodiment taken along line  5 - 5  in  FIG. 3 ; 
         FIG. 6  is still another sectional view of the first preferred embodiment taken along line  6 - 6  in  FIG. 3 ; 
         FIG. 7  is an exploded perspective view of a torque-adjusting unit and a resilient member of a friction-providing unit of the first preferred embodiment; 
         FIG. 8  is an exploded perspective view of the torque-adjusting unit and a modified resilient member of the friction-providing unit of the first preferred embodiment; 
         FIGS. 9 to 22  illustrate an assembling process of the first preferred embodiment; 
         FIG. 23  is an exploded perspective view of a second preferred embodiment of the hinge device according to the invention; 
         FIG. 24  is a sectional view of the second preferred embodiment; 
         FIG. 25  is another sectional view of the second preferred embodiment taken along line  25 - 25  in  FIG. 24 ; 
         FIG. 26  is an exploded perspective view of a third preferred embodiment of the hinge device according to the invention; 
         FIG. 27  is a sectional view of the third preferred embodiment; 
         FIG. 28  is an exploded perspective view of a fourth preferred embodiment of the hinge device according to the invention; 
         FIG. 29  is an assembled top view of the fourth preferred embodiment; 
         FIG. 30  is a sectional view of the fourth preferred embodiment taken along line  30 - 30  in  FIG. 29 ; 
         FIG. 31  is another sectional view of the fourth preferred embodiment taken along line  31 - 31  in  FIG. 29 ; 
         FIG. 32  is an exploded perspective view of a fifth preferred embodiment of the hinge device according to the invention; 
         FIG. 33  is a sectional view of the fifth preferred embodiment; 
         FIG. 34  is an exploded perspective view of a sixth preferred embodiment of the hinge device according to the invention; 
         FIG. 35  is a sectional view of the sixth preferred embodiment; 
         FIG. 36  is another sectional view of the sixth preferred embodiment taken along line  36 - 36  in  FIG. 35 ; 
         FIG. 37  is a partly sectional view of a seventh preferred embodiment of the hinge device according to the invention, illustrating a first leaf at a zero-degree angular position relative to a second leaf; 
         FIG. 38  is a side view of the seventh preferred embodiment, illustrating the first leaf at the zero-degree angular position relative to the second leaf; 
         FIG. 39  is an exploded perspective view of a friction-providing unit of the seventh preferred embodiment; 
         FIG. 40  is another side view of the seventh preferred embodiment, illustrating the first leaf at a 45-degree angular position relative to the second leaf; 
         FIG. 41  is another partly sectional view of the seventh preferred embodiment, illustrating the first leaf at the 45-degree angular position relative to the second leaf; 
         FIG. 42  is a sectional view of an eighth preferred embodiment of the hinge device according to the invention, illustrating a first leaf at a zero-degree angular position relative to a second leaf; 
         FIG. 43  is an exploded perspective view of a friction-providing unit of the eighth preferred embodiment; 
         FIG. 44  is another partly sectional view of the eighth preferred embodiment, illustrating the first leaf at a 45-degree angular position relative to the second leaf; 
         FIG. 45  is an exploded perspective view of a ninth preferred embodiment of the hinge device according to the invention; 
         FIG. 46  is a sectional view of the ninth preferred embodiment; 
         FIG. 47  is another sectional view of the ninth preferred embodiment taken along line  47 - 47  in  FIG. 46 ; 
         FIG. 48  is still another sectional view of the ninth preferred embodiment taken along line  48 - 48  in  FIG. 47 ; 
         FIG. 49  is an exploded perspective view of a tenth preferred embodiment of the hinge device according to the invention; 
         FIG. 50  is a sectional view of the tenth preferred embodiment; 
         FIG. 51  is another sectional view of the tenth preferred embodiment taken along line  51 - 51  in  FIG. 50 ; and 
         FIG. 52  is still another sectional view of the tenth preferred embodiment taken along line  52 - 52  in  FIG. 51 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 2 to 4 , the first preferred embodiment of a hinge device according to the present invention includes a hinge unit  20 , a torque-providing unit  30 , a torque-adjusting unit  40 , and a friction-providing unit  50 . 
     The hinge unit  20  includes a first leaf  21  adapted to be mounted to a door panel (not shown), a second leaf  22  adapted to be mounted to a door frame (not shown), and a knuckle unit  280 . The knuckle unit  280  includes a first knuckle  212 , a pair of circular outer knuckles  213 ,  216 , and a pair of second knuckles  222 ,  224 . The first knuckle  212  and the outer knuckles  213 ,  216  are provided to the first leaf  21 . The second knuckles  222 ,  224  are provided to the second leaf  22 . The second knuckle  222  is disposed between and is coupled pivotally to the first knuckle  212  and the outer knuckle  213 , and the second knuckle  224  is disposed between and is coupled pivotally to the first knuckle  212  and the outer knuckle  216 , such that the first leaf  21  is pivotable relative to the second leaf  22 . The first knuckle  212 , the outer knuckles  213 ,  216 , and the second knuckles  222 ,  224  define cooperatively a channel unit  250  that extends along an axis (L 1 ). In this embodiment, the outer knuckles  213 ,  216  are formed respectively with first and second grooves  214 ,  217 , each of which extends circumferentially by 180 degrees. The first knuckle  212  has an internal surface with axially opposite ends that are adjacent respectively to the second knuckles  222 ,  224  and that are formed respectively with a pair of stepped surface portions  218 ,  215 . In this embodiment, a portion of the channel unit  250  within the second knuckle  222  is an elliptical channel portion  223 , and another portion of the channel unit  250  within the second knuckle  224  is also an elliptical channel portion  225 . The hinge unit  20  further includes a plurality of spacer components  23  each disposed between a corresponding adjacent pair of the first knuckle  212 , the outer knuckles  213 ,  216  and the second knuckles  222 ,  224 , such that the first leaf  21  can be pivoted smoothly relative to the second leaf  22 . In this embodiment, each of the spacer components  23  is made mainly of polytetrafluoroethylene (PTFE). 
     The torque-providing unit  30  includes a first barrel  31 , a torsion spring  32 , a positioning nut  33 , a threaded limiting component  34 , a first C-ring  35 , a first enclosing component  36 , and a first enclosing bolt  37 . The first barrel  31  extends in the outer knuckle  216  and the second knuckle  224  of the hinge unit  20 , and has an elliptical barrel body extending fittingly into the elliptical channel portion  225  in the second knuckle  224  so as to be secured to the second knuckle  224 . Since the outer knuckle  216  is circular, it can be rotated freely relative to the first barrel  31 . The barrel body of the first barrel  31  is formed with a through hole  311  registered with the second groove  217  in the outer knuckle  216 . The torsion spring  32  is disposed in the first barrel  31  and has opposite first and second ends  322 ,  321 . The positioning nut  33  is disposed in the first barrel  31 , is secured to the first end  322  of the torsion spring  32 , and is formed with a threaded positioning hole  331  registered with the second groove  217  in the outer knuckle  216  and the through hole  311  in the barrel body of the first barrel  31 . Referring further to  FIG. 5 , the threaded limiting component  34  extends threadedly through the threaded positioning hole  331  in the positioning nut  33 , and has one end opposite to the positioning nut  33  and extending outwardly of the second groove  217  via the through hole  311  for maintaining the positioning nut  33  at an axial position relative to the first barrel  31 . The first C-ring  35  is disposed in the first barrel  31 , and engages an annular groove unit  317  in an inner surface of the first barrel  31  and an annular groove unit  337  in an outer surface of the positioning nut  33  for retaining the positioning nut  33  within the first barrel  31 . The first enclosing component  36  is disposed at an end of the outer knuckle  216  opposite to the second knuckle  224 . The first enclosing bolt  37  extends through the first enclosing component  36  and engages threadedly the positioning nut  33  so as to cover the end of the outer knuckle  216 . Since the positioning nut  33  is retained within and positioned relative to the first barrel  31 , and since the first barrel is secured to the second knuckle  224 , the first end  322  of the torsion spring  32  is secured to the second knuckle  224 . 
     The torque-adjusting unit  40  includes a cam mechanism  41  and a shaft  42 . 
     The cam mechanism  41  is disposed in the first knuckle  212 , and includes a hollow cam  411 , a hollow cam follower  412 , and a resilient component  413 . Referring further to  FIGS. 7 and 20 , the cam  411  is formed with a pair of engaging blocks  4111  that are angularly spaced apart from each other, that project radially and outwardly therefrom, and that engage the stepped surface portion  218  of the internal surface of the first knuckle  212  such that the cam  411  is coupled co-rotatably to and is axially movable relative to the first knuckle  212 . The cam  411  is further formed with a plurality of angularly spaced-apart protrusions  4112  protruding in a direction parallel to the axis (L 1 ) from an end thereof. Each of the protrusions  4112  has a steep slope face  4118  and a gentle slope face  4119  opposite to the steep slope face  4118 . The cam follower  412  is disposed rotatably in the stepped surface portion  215  of the first knuckle  212 , and has a central hole  4121  extending therethrough along the axis (L 1 ), and a plurality of recesses  4122  formed at an end thereof adjacent to the cam  411  and engaging respectively and removably the protrusions  4112  of the cam  411 . Each of the recesses  4122  is defined by a steep slope face  4128  and a gentle slope face  4129 . The resilient component  413  is disposed for biasing resiliently the cam  411  toward the cam follower  412 . 
     The shaft  42  extends along the axis (L 1 ) in the channel unit  250 , and includes first and second shaft segments  421 ,  422  coupled co-rotatably to each other. The first shaft segment  421  extends from the first knuckle  212  the outer knuckle  213  through the second knuckle  222 , and has a non-circular insert end portion  4211 . The second shaft segment  422  extends from the first knuckle  212  into the outer knuckle  216  through the second knuckle  224 , and has a hollow coupling end portion  4223  extending fittingly through the central hole  4121  in the cam follower  412  so as to be coupled co-rotatably to the cam follower  412 . The insert end portion  4211  of the first shaft segment  421  is inserted fittingly into the coupling end portion  422  of the second shaft segment  422  so as to be coupled co-rotatably to the second shaft segment  422  and the cam follower  412 . The coupling end portion  4223  of the second shaft segment  4223  is formed with a slot  4225  for retaining the second end  321  of the torsion spring  32  of the torque-providing unit  30  therein, such that the cam follower  412  is coupled co-rotatably to the second end  321  of the torsion spring  32 . The second shaft segment  4223  further has a driven end portion  4221  opposite to the coupling end portion  4223  and formed with an accessible hexagonal tool driven hole  4222  so that the shaft  42  is capable of being driven to rotate. 
     Referring once again to  FIGS. 2 to 4 , and further referring to  FIG. 7 , the friction-providing unit  50  includes a second barrel  51 , a threaded limiting member  52 , a friction-providing component  53 , a resilient member  54 , an adjusting component  55 , a second C-ring  56 , a second enclosing component  57 , and a second enclosing bolt  58 . 
     The second barrel  51  extends in the outer knuckle  213  and the second knuckle  222  of the hinge unit  20 , and has an elliptical barrel body extending fittingly into the elliptical channel portion  223  in the second knuckle  222  so as to be coupled co-rotatably to the second knuckle  222 . The barrel body of the second barrel  51  is formed with an internal flange  515  projecting radially and inwardly therefrom, and having a first side  5151  against which the resilient component  413  resiliently abuts, and a second side  5152  which is opposite to the first side  5151  along the axis (L 1 ). The barrel body of the second barrel  51  is further formed with a threaded hole  511  registered with the first groove  214  in the outer knuckle  213 . 
     In this embodiment, the friction-providing component  53  is disposed within the second barrel  51 , is provided co-rotatably on the shaft  42 , and includes a flange  531 , a pair of first protrusions  533 , a pair of second protrusions  535 , and a pair of first and second brake plates  532 ,  534 . The flange  531  projects radially and outwardly from the first shaft segment  421  of the shaft  42 , and has opposite side surfaces. The first protrusions  553  protrude from one of the side surfaces of the flange  531 , while the second protrusions  535  protrude from the other one of the side surfaces of the flange  531 . The second brake plate  534  is disposed between the flange  531  and the second side  5152  of the internal flange  515  of the second barrel  51 , and the first brake plate  532  is disposed at a side of the flange  531  opposite to the second brake plate  534  along the axis (L 1 ). 
     In this embodiment, the resilient member  54  is a compression spring made of a music wire, and is disposed at one side of the first brake plate  532  opposite to the internal flange  515  of the second barrel  51  along the axis (L 1 ). Moreover, the actual form of the resilient member  54  is not limited. As illustrated in  FIG. 8 , a possible modified form of the resilient member  54  includes a plurality of disc springs. 
     The adjusting component  55  is disposed in the second barrel  51 , has an external thread engaging an internal thread in an inner surface of the second barrel  51 , and has an end that abuts against the resilient member  54  and an opposite end that is formed with an accessible hexagonal driven hole  551  (see  FIG. 4 ) so that the adjusting component  55  is capable of being driven to move toward and away from the friction-providing component  53  along the axis (L 1 ). When the adjusting component  55  is moved toward the friction-providing component  53 , it drives the resilient member  54  to abut resiliently against the first brake plate  532 , such that the first and second brake plates  532 ,  534  are biased by the resilient member  54  to press against the first and second protrusions  533 ,  535  at the flange  531 , thereby resulting in friction against the rotation of the shaft  42 . In this embodiment, the first and second brake plates  532 ,  534  are made from a material softer than the first and second protrusions  533 ,  535 , and are able to deform to abut fittingly against the first and second protrusions  533 ,  535 , thereby resulting in a relatively large friction between the flange  531  and the first and second brake plates  532 ,  534 . 
     Referring further to  FIG. 6 , the threaded limiting member  52  extends threadedly through the threaded hole  511  in the barrel body of the second barrel  51  to press against the adjusting component  55  for locking the adjusting component  55  relative to the second barrel  51 , and has one end opposite to the adjusting component  55  and extending outwardly of the second groove  214  in the outer knuckle  213  of the knuckle unit  280  of the hinge unit  20  via the threaded hole  511 . 
     The second C-ring  56  is disposed in the second barrel  51 , and engages an annular groove unit  517  in the inner surface of the second barrel  51  and an annular groove unit  557  in an outer surface of the adjusting component  55  for retaining the adjusting component  55  within the second barrel  51 . The second enclosing component  57  is disposed at an end of the outer knuckle  213  opposite to the second knuckle  222 , and extends into the second barrel  51 . The second enclosing bolt  58  extends through the second enclosing component  57  and engages threadedly the adjusting component  55  so as to cover the end of the outer knuckle  213 . 
     The assembling process of the first preferred embodiment of this invention will now be described in the following. 
     As shown in  FIG. 9 , the first step of the assembling process is to sleeve the second brake plate  534  of the friction-providing component  53  on the first shaft segment  421  of the shaft  42  to abut against the second protrusions  535  at the flange  531  of the friction-providing component  53 , and to insert the first shaft segment  421  and the second brake plate  534  into the second barrel  51  via an end of the second barrel  51 . 
     As shown in  FIG. 10 , the second step is to insert the resilient component  413  into the second barrel  51  via an opposite end of the second barrel  51  to sleeve on the first shaft segment  421 . 
     Referring to  FIG. 11 , the third step is to couple the first leaf  21  to the second leaf  22 , and to dispose the spacer components  23  between the first and second leaves  21 ,  22 . 
     Referring to  FIGS. 12 and 13 , the fourth step is to insert the cam  411 , a washer  24 , and the assembly of the second barrel  51 , the first shaft segment  421 , the second brake plate  534 , and the resilient component  413  into the outer knuckle  213  and the second knuckle  222  of the hinge unit  20 . 
     As shown in  FIGS. 14 and 15 , the fifth step is to sleeve the first brake plate  532  on the first shaft segment  421  of the shaft  42  to abut against the first protrusions  533 , to insert the resilient member  54  and another washer  24  into the second barrel  51  in such a manner to sleeve the same on the first shaft segment  421 , and to insert the adjusting component  55  threadedly into the second barrel  51 , and to extend threadedly the threaded limiting member  52  into the threaded hole  511  in the second barrel  51  via the second groove  214  in the outer knuckle  213 , thereby locking the adjusting component  55  relative to the second barrel  51 . 
     Referring to  FIG. 16 , the sixth step is to insert the first barrel  31  and another washer  24  into the outer knuckle  216  and the second knuckle  224  of the knuckle unit  20 . 
     As shown in  FIGS. 17 and 18 , the seventh step is to sleeve the torsion spring  32  on the second shaft segment  422 , to insert the second end  321  of the torsion spring  32  into the slot  4225  in the coupling end portion  4223  of the second shaft segment  422 , and to sleeve the cam follower  412  on the coupling end portion  4223  of the second shaft segment  422  for securing the second end  321  of the torsion spring  32  to the second shaft segment  422 . 
     Referring to  FIG. 19 , the eighth step is to insert the assembly of the second shaft segment  422 , the torsion spring  32 , and the cam follower  412  into the first barrel  31 , to insert the positioning nut  33  into the first barrel  31 , and to extend threadedly the threaded limiting component  34  into the positioning hole  331  in the positioning nut  33  via the first groove  217  in the outer knuckle  216  and the through hole  311  in the first barrel  31 , thereby positioning the positioning nut  33  relative to the first barrel  31 . Consequently, the second shaft segment  422  is coupled to the first shaft segment  421  via the engagement between the coupling end portion  4223  of the second shaft segment  422  and the insert end portion  4211  of the first shaft segment  421 , and the cam  411  is biased resiliently by the resilient component  413  to be coupled to the cam follower  412  (see  FIGS. 20 and 21 ). 
     Referring to  FIG. 22 , the ninth step is to couple the first C-ring  35 , the first enclosing component  36  and the first enclosing bolt  37  to the first barrel  31 , and to couple the second C-ring  56 , the second enclosing component  57  and the second enclosing bolt  58  to the second barrel  51  for completing the assembling process. 
     In use, during the door-opening process, the first leaf  21  is pivoted relative to the second leaf  22 , while the first knuckle  212  and the outer knuckles  213 ,  316  are rotated in a first rotational direction (R 1 ) (see  FIG. 2 ) relative to the second knuckles  222 ,  224 . Simultaneously, the cam  411  of the cam mechanism  41  of the torque-adjusting unit  4  is driven to rotate in the first rotational direction (R 1 ), and engages the cam follower  412  with the protrusions  4112  of the cam  411  engaging respectively the recesses  4122  in the cam follower  412  through abutment of the steep slope face  4118  of each of the protrusions  4112  of the cam  411  against the steep slope face  4128  defining a respective one of the recesses  4122 , such that the cam follower  412  is driven to rotate in the first rotational direction (R 1 ) together with the cam  411 . Since the second end  321  of the torsion spring  32  of the torque-providing unit  30  is coupled co-rotatably to the shaft  42  of the torque-adjusting unit  40  and the cam follower  412 , and since the first end  322  of the torsion spring  32  is secured to the second knuckle  224 , the rotation of the cam follower  412  twists the torsion spring  32 . 
     When a force for opening the door is released, the cam follower  412  is driven by a restoring force of the torsion spring  32  to automatically rotate in a second rotational direction (R 2 ) (see  FIG. 2 ) opposite to the first rotational direction (R 1 ) so as to drive the cam  411  to rotate in the second rotational direction (R 2 ) through abutment of the steep slope face  4128  of each of the recesses  4122  against the steep slope face  4118  of a respective one of the protrusions  4112  of the cam  411 , thereby driving the first knuckle  212  to rotate in the second rotational direction (R 2 ) relative to the second knuckles  222 ,  224 , and eventually driving the first leaf  21  to pivot reversely relative to the second leaf  22  to complete a door-closing process. 
     Moreover, before the door is opened, by disengaging the first enclosing bolt  37  from the positioning nut  33  and removing the first enclosing component  36  from the first barrel  31 , a user is able to insert a hand tool (such as a hex wrench) into the tool driven hole  4221  in the second shaft segment  422  of the shaft  42  and operate the hand tool to rotate the shaft  42  in the first rotational direction (R 1 ), thereby twisting the torsion spring  32  so as to increase the torque of the torsion spring  32 . At the same time, the cam follower  412  is also driven to rotate in the first rotational direction (R 1 ) relative to the cam  411 , thereby biasing the cam  411  to move away from the cam follower  412  along the axis (L 1 ) against a resilient force of the resilient component  413  through sliding movement of each of the gentle slope faces  4129  of the cam follower  412  relative to the gentle slope face  4119  of the respective one of the protrusions  4112  of the cam  411 . After the torque adjustment, the hand tool is removed from the tool driven hole  4221 , so that a restoring force of the resilient component  413  biases the cam  411  to press against the cam follower  412 , thereby preventing the cam follower  412  from being rotated in the second rotational direction (R 2 ) by a restoring force of the torsion spring  32 . Therefore, the adjusted torque of the torsion spring  32  can be maintained. 
     Furthermore, before the door is opened, by disengaging the second enclosing bolt  58  from the adjusting component  55  and removing the second enclosing component  57  from the second barrel  51 , the user is able to insert the hand tool into the driven hole  551  in the adjusting component  55  and operate the hand tool to drive the adjusting component  55  to move threadably toward the friction-providing component  53  of the friction-providing unit  50  along the axis (L 1 ), thereby increasing the resilient force of the resilient member  54  that is exerted to the first and second brake plates  532 ,  534 , such that the friction between the first brake plate  532  and the first protrusions  533  on the flange  531  as well as the friction between the second brake plate  534  and the second protrusions  535  on the flange  531  is increased so as to slow down the rotation of the shaft  42  and the cam follower  412  in the second rotational direction (R 2 ) due to the untwisting action of the torsion spring  32 . As such, the rotation of the cam  411  and the first knuckle  212  in the second rotational direction (R 2 ) is slowed down, so that the pivoting movement of the first leaf  21  relative to the second leaf  22  during the door-closing process is also slowed down to prevent the door panel from severely striking the door frame. On the contrary, the adjusting component  55  can also be rotated in the same manner to move threadably away from the friction-providing component  53  along the axis (L 1 ), thereby decreasing the friction between the first brake plate  532  and the first protrusions  533  as well as the friction between the second brake plate  534  and the second protrusions  535  so as to speed up the rotation of the shaft  42  and the cam follower  412  in the second rotational direction (R 2 ), and to eventually speed up the pivoting movement of the first leaf  21  relative to the second leaf  22  during the door-closing process. 
     From the aforementioned description, the advantages of the hinge device according to the present invention can be summarized as follows: 
     1. By virtue of the untwisting action of the torsion spring  32 , the first leaf  21  can be automatically driven to pivot relative to the second leaf  22  to result in the door-closing process. 
     2. By operating the torque-adjusting unit  40  to rotate the shaft  42  in the first rotational direction (R 1 ), the torque of the torsion spring  32  of the torque-providing unit  30  can be easily adjusted. Moreover, the shaft  42  can be rotated freely for 360 degrees during the torque adjustment so as to twist or untwist the torsion spring  32 . 
     3. By operating the friction-providing unit  50 , the speed of the pivoting movement of the first leaf  21  relative to the second leaf  22  can be properly adjusted. 
     4. By virtue of the spacer components  23 , the first leaf  21  can be pivoted smoothly relative to the second leaf  22 . 
     As shown in  FIGS. 23 to 25 , the second preferred embodiment of the hinge device  100  according to the present invention has a structure similar to that of the first preferred embodiment. The main difference between this embodiment and the previous embodiment resides in the following. The hinge device  100  includes a hinge unit  110 , a torque-providing unit  120 , a torque-adjusting unit  130 , and a friction-providing unit  140 . 
     The hinge unit  110  includes a first leaf  111  adapted to be mounted to a door panel (not shown), a second leaf  112  adapted to be mounted to a door frame (not shown), and a knuckle unit  115 . The knuckle unit  115  includes a pair of first knuckles  1151  provided to the first leaf  111 , and a pair of second knuckles  1152  provided to the second leaf  112  and coupled to the first knuckles  1151  such that the first leaf  111  is pivotable relative to the second leaf  112 . The knuckle unit  115  has an inner surrounding surface unit  119  (see  FIG. 25 ) defining a channel unit  118  therein. In this embodiment, a portion of the channel unit  118  that is within the right first knuckle  1151  is an elliptical channel portion  113 . The torque-providing unit  120  includes a torsion spring  121  that has opposite first and second ends  1211 ,  1212 . The torque-adjusting unit  130  includes a hollow cam  131 , a cam follower  132 , a resilient component  133 , and a shaft  134 . The cam  131  is coupled co-rotatably to the left first knuckle  1151  and is formed with a plurality of recesses  1311 . The cam follower  132  is rotatable relative to the first knuckles  1151  and is secured to the first end  1211  of the torsion spring  121 . The cam follower  132  has a first end portion extending rotatably into the cam  131 , and is formed with an accessible hexagonal hole  1322  and a plurality of protrusions  1321  for engaging respectively and removably the recesses  1311  in the cam  131 . The cam follower  132  further has a second end portion opposite to the first end portion along an axis (L 2 ) and is formed with a receiving hole  1323 . The resilient component  133  is disposed within the receiving hole  1323 . The shaft  134  is secured to the second end  1212  of the torsion spring  121 , and has a cylindrical end  1341  which extends movably into the receiving hole  1323  and on which the resilient component  133  is sleeved, such that the cam follower  132  is biased resiliently by the resilient component  133  toward the cam  131 . The shaft  134  further has a coupling end  1342  opposite to the cylindrical end  1341  and formed with a flat engaging block. 
     The friction-providing unit  140  includes a rod member  141  that extends along the axis (L 2 ) in the portion of the channel unit  118  (i.e., the elliptical channel portion  113 ), a pair of friction-providing blocks  143  that are disposed movably and respectively at diametrically opposite sides of the rod member  141 , and a block-engaging spring  142  that extends transversely through the rod member  141  and that has opposite ends connected respectively to the friction-providing blocks  143  for biasing resiliently and outwardly the friction-providing blocks  143  to move into frictional contact with the inner surrounding surface unit  119  of the knuckle unit  115 . The rod member  141  has opposite ends along the axis (L 2 ) formed respectively with a pair of engaging slots  1411 ,  1412 . The friction-providing unit  140  further includes a coupling block  135  secured to one of the second knuckles  1152  of the knuckle unit  115 , and having an engaging end  1351  formed with a flat engaging block. The engaging block of the coupling end  1342  of the shaft  134  is inserted fittingly into the engaging slot  1412  in the rod member  141  for coupling the shaft  134  to the rod member  141 . The engaging block of the engaging end  1351  of the coupling block  135  is inserted fittingly into the engaging slot  1411  in the rod member  141  for coupling the rod member  141  to the coupling block  135 . 
     During the door-opening process, the first knuckles  1151  are rotated in the first rotational direction (R 1 ) relative to the second knuckles  1152 , and the cam  131  is rotated together with the first knuckles  1151  so as to drive the cam follower  132  to rotate together therewith through engagement between the protrusions  1321  of the cam follower  132  and the recesses  1311  in the cam  131 . 
     Meanwhile, the assembly of the shaft  134  and the friction-providing unit  140  is not rotated since the coupling block  135  is secured to the one of the second knuckles  1152 . Since the first end  1211  of the torsion spring  121  is secured to the cam follower  132  while the second end  1212  of the torsion spring  121  is secured to the shaft  134 , the torsion spring  121  is twisted during the door-opening process. 
     Before the door-opening process, by inserting a hand tool into the hexagonal hole  1322  in the cam follower  132 , the cam follower  132  is accessibly operable to rotate in the first rotational direction (R 1 ) so as to twist the torsion spring  121 , thereby increasing the torque of the torsion spring  121 . Moreover, the cam follower  132  is further accessibly operable to separate from the cam  131  along the axis (L 2 ) so as to untwist the torsion spring  121 , thereby allowing readjustment of the torque of the torsion spring  121 . The resilient component  133  is compressed when the cam follower  132  is separated from the cam  131 . The cam follower  132  is biased by a restoring force of the resilient component  133  to move back to re-engage the cam  131  after the torque adjustment. 
     During the pivoting movement of the first leaf  111  relative to the second leaf  112 , one of the first knuckles  1151  defining the elliptical channel portion  113  is rotated relative to the rod member  141 , so as to vary angular orientation of the rod member  141  relative to the elliptical channel portion  113  and, thus, the biasing force of the block-engaging spring  142  for biasing the friction-providing blocks  143  into frictional contact with the inner surrounding surface unit  119 , thereby automatically changing the speed of the pivoting movement of the first leaf  111 . The second preferred embodiment has the same advantages as those of the first preferred embodiment. 
     As shown in  FIGS. 26 and 27 , the third preferred embodiment of the hinge device  200  according to the present invention has a structure similar to that of the first preferred embodiment. In this embodiment, the hinge device  200  comprises a hinge unit  210 , a torque-providing unit  220 , and a torque-adjusting unit  230 . The main difference between this embodiment and the first preferred embodiment resides in that the friction-providing unit  50  of the first preferred embodiment is omitted in this embodiment. 
     As shown in  FIGS. 28 to 31 , the fourth preferred embodiment of the hinge device  300  according to the present invention has a structure similar to that of the first preferred embodiment. In this embodiment, the hinge device  300  comprises a hinge unit  380 , a torque-providing unit  320 , a torque-adjusting unit  330 , and a friction-providing unit  340 . The main difference between this embodiment and the first preferred embodiment resides in the following. The hinge unit  380  includes a first leaf  381 , a second leaf  383 , a first knuckle  382  connected to a middle portion of a side of the first leaf  381 , and a pair of second knuckles  384  connected to a side of the second leaf  383  and coupled respectively and pivotally to opposite ends of the first knuckle  382 . The hinge unit  380  further includes a pair of bearing units  385  disposed between the first and second leaves  381 ,  382 . In this embodiment, each of the bearing units  385  has a plurality of roller grooves  3851  formed in an outer surrounding surface of a respective one of the second knuckles  384 , a plurality of rollers  3852  retained rotatably and respectively in the roller grooves  3851 , and a barrel member  3853  sleeved rotatably on the rollers  3852  and welded to the first leaf  381 . The fourth preferred embodiment has the same advantages as those of the first preferred embodiment. 
     As shown in  FIGS. 32 and 33 , the fifth preferred embodiment of the hinge device  400  according to the present invention has a structure similar to that of the fourth preferred embodiment. The main difference between this embodiment and the fourth preferred embodiment resides in the configuration of the bearing unit. In this embodiment, each of the bearing units  455  includes a wear-resisting copper ring  453  sleeved on a respective one of the second knuckles  452 , and a barrel member  457  sleeved rotatably on the wear-resisting copper ring  453  and welded to the first leaf  454 . 
     Referring to  FIGS. 34 to 36 , the sixth preferred embodiment of the hinge device  500  according to the present invention has a structure similar to that of the second preferred embodiment. In this embodiment, the hinge device  500  comprises a hinge unit  570 , a torque-providing unit  520 , a torque-adjusting unit  530  and a friction-providing unit  540 . 
     The hinge unit  570  includes first and second leaves  571 ,  572 , and a knuckle unit  575 . The knuckle unit  575  includes a pair of first knuckles  5751  provided to the first leaf  571 , and a pair of second knuckles  5752  provided to the second leaf  572  and coupled to the first knuckles  5751  such that the first leaf  571  is pivotable relative to the second leaf  572 . The knuckle unit  575  has an inner surrounding surface unit  579  defining a channel unit  578  therein. In this embodiment, a portion of the channel unit  578  that is within the right first knuckle  5751  is an elliptical channel portion  573 . 
     The torque-adjusting unit  580  includes a hollow cam  581 , a cam follower  582 , a resilient component  584 , a shaft  583 , a first C-ring  585 , and a first enclosing bolt  586 . The cam  581  is coupled co-rotatably the left first knuckle  5751  and is formed with a plurality of recesses  5811 . The cam follower  582  is rotatable relative to the first knuckles  5751 . The cam follower  582  has a left end portion  5825  extending rotatably into the cam  581 , is formed with an accessible hexagonal hole  5821  and a plurality of protrusions  5822  for engaging respectively and removably the recesses  5811  in the cam  581 . The cam follower  582  further has a right end portion  5826  opposite to the left end portion  5825  along an axis (L 3 ) and formed with a receiving hole  5823 . The resilient component  584  is disposed within the receiving hole  5823 . The shaft  583  has a cylindrical end which extends movably into the receiving hole  5823  and on which the resilient component  584  is sleeved, such that the cam follower  582  is biased resiliently by the resilient component  584  toward the cam  581 . The shaft  583  further has a coupling end opposite to the cylindrical end along the axis (L 3 ) and formed with an engaging groove  5831 . The first C-ring  585  and the first enclosing bolt  586  are disposed within the channel unit  578  for retaining the cam  581  within the channel unit  578 . The first enclosing bolt  586  is formed with an internal hexagonal hole  5861  extending therethrough along the axis (L 3 ). The torque-providing unit  520  includes a torsion spring  521  having opposite ends secured respectively to the cam follower  582  and the shaft  583 . 
     The friction-providing unit  540  includes a rod member  541 , a pair of friction-providing blocks  542 , a coupling pin  544 , a block-engaging spring  543 , a cam component  546 , a resilient component  545 , a threaded locking component  547 , a second C-ring  548 , and a second enclosing bolt  549 . 
     The rod member  541  extends along the axis (L 3 ) in the portion of the channel unit  578  (i.e., the elliptical channel portion  573 ), and has a first longitudinal end  5411  formed with a rectangular block that engages the engaging groove  5831  in the shaft  583 , and a second longitudinal end  5412  opposite to the first engaging end  5411  along the axis (L 3 ), secured to one of the second knuckles  5752 , and formed with a pair of cam surfaces  5415  (only one is shown). The rod member  541  further has a pair of inclined outer surfaces  5413  formed respectively at diametrically opposite sides thereof between the first and second longitudinal ends  5411 ,  5412 , and an elongated through hole  5414  extending transversely through the inclined outer surfaces  5413 . The friction-providing blocks  542  are disposed movably and respectively at diametrically opposite sides of the rod member  541 , and are disposed respectively adjacent to the inclined outer surfaces  5413 . Each of the friction-providing blocks  542  is formed with a pin hole  5421  extending transversely therethrough. The coupling pin  544  extends from the pin hole  5421  in one of the friction-providing blocks  542  into the pin hole  5421  in the other one of the friction-providing blocks  542  via the elongated through hole  5414  in the rod member  541 . The block-engaging spring  543  is sleeved on the coupling pin  544 , and extends through the elongated through hole  5414  in the rod member  541  with opposite ends inserted respectively into the pin holes  5421  in the friction-providing blocks  542  for biasing resiliently and outwardly the friction-providing blocks  542  to move into frictional contact with the inner surrounding surface unit  579  of the knuckle unit  575 . The elongated through hole  5414  in the rod member  541  has a width larger than that of the block-engaging spring  543  such that the rod member  541  is axially movable relative to the friction-providing blocks  542 . The cam component  546  is disposed in one of the second knuckles  5752  secured to the rod member  541 , and has a pair of protrusions  5461  abutting rotatably and respectively against the cam surfaces  5415  of the rod member  541 , and a hexagonal driven hole  5462  extending therethrough. The resilient component  545  is sleeved on the rod member  541  for biasing the rod member  541  to abut against the cam component  546 . The second C-ring  548  and the second enclosing bolt  549  are disposed within the channel unit  578  for retaining the cam component  546  within the channel unit  578 . The second enclosing bolt  549  is formed with an internal hexagonal hole  5491  extending therethrough along the axis (L 3 ). The threaded locking component  547  extends through the one of the second knuckles  5752  to press against the cam component  546  for locking the cam component  546  and, thus, the rod member  541  relative to the one of the second knuckles  5752 . 
     In this embodiment, the torsion spring  521  is twisted during the door-opening process, and a restoring force of the torsion spring  521  automatically closes the door in the same manner as the second preferred embodiment. 
     Before the door-opening process, by inserting a hand tool into the hexagonal hole  5821  in the cam follower  582  via the internal hexagonal hole  5861  of the first enclosing bolt  586 , the cam follower  582  is accessibly operable to rotate in the same manner as the second preferred embodiment so as to twist the torsion spring  521 , thereby increasing the torque of the torsion spring  521 . Moreover, the cam follower  582  is further accessibly operable to move in the same manner as the second preferred embodiment to untwist the torsion spring  521 , thereby allowing readjustment of the torque of the torsion spring  521 . 
     During the pivoting movement of the first leaf  571  relative to the second leaf  572 , one of the first knuckles  5751  that defines the elliptical channel portion  573  is rotated relative to the rod member  541 , so as to vary angular orientation of the rod member  541  relative to the elliptical channel unit  573  and, thus, the biasing force of the block-engaging spring  543  for biasing the friction-providing blocks  542  into frictional contact with the inner surrounding surface unit  579 , thereby automatically adjusting the speed of the pivoting movement of the first leaf  571  relative to the second leaf  572 . Moreover, by loosening the threaded locking component  547  and inserting the hand tool into the driven hole  5462  in the cam component  546  via the internal hexagonal hole  5491  of the second enclosing bolt  549 , the cam component  546  is rotatable to result in axial movement of the rod member  541  away from the cam component  546  relative to the friction-providing blocks  542  through sliding movement of the protrusions  5461  of the cam component  546  relative to the cam surfaces  5415  of the rod member  541 . The axial movement of the rod member  541  then results in radial and outward movement of the friction-providing blocks  542  through sliding movement of the friction-providing blocks  542  relative to the inclined outer surfaces  5413  of the rod member  541 , thereby increasing friction between the friction-providing blocks  542  and the inner surrounding surface unit  579  of the knuckle unit  575 . Furthermore, the cam component  546  can be further rotated reversely to permit the rod member  541  to be biased by the resilient component  545  to move toward the cam component  546  relative to the friction-providing blocks  542  to thereby decrease the friction between the friction-providing blocks  542  and the inner surrounding surface unit  579  of the knuckle unit  575 . Therefore, the friction between the friction-providing blocks  542  and the inner surrounding surface unit  579  of the knuckle unit  575  can also be manually adjusted. 
     Referring to  FIGS. 37 to 39 , the seventh preferred embodiment of the hinge device  600  according to the present invention has a structure similar to that of the first preferred embodiment. The main difference between this embodiment and the first preferred embodiment resides in the configuration of the friction-providing unit. In this embodiment, the friction-providing unit  630  includes a flange  6311 , a pair of ring plates  632 , and a pair of resilient members  633 . The flange  6311  projects radially and outwardly from the shaft  631  and has two side surfaces opposite to each other along an axis (L 4 ). Each of the side surfaces is formed with a plurality of corrugations  6312  each having a plurality of alternately arranged thicker and thinner portions. The ring plates  632  are sleeved rotatably on the shaft  631 . Each of the ring plates  632  has a side plate surface formed with a pair of protrusions  6321  that are rotatable to contact respectively two corresponding ones of the corrugations  6312  in a corresponding one of the side surfaces of the flange  6311 . In this embodiment, each of the resilient members  633  includes a plurality of disc springs. The resilient members  633  abut resiliently and respectively against the ring plates  632 . 
     Before the door-opening process, the first leaf  611  is disposed at a zero-degree angular position (see  FIG. 38 ) relative to the second leaf  612 , where each of the protrusions  6321  of the ring plates  632  abuts against a respective one of the thicker portions of the corresponding corrugation  6312  (see  FIG. 37 ). During the door-opening process, for example, when the first leaf  611  is pivoted from the zero-degree angular position to a 45-degree angular position (see  FIG. 40 ) relative to the second leaf  612 , the shaft  631  and the flange  6311  are rotated relative to the ring plates  632 , such that each of the protrusions  6321  of the ring plates  632  slides on the corresponding corrugation  6312  from the respective one of the thicker portions of the corresponding corrugation  6312  onto a respective one of the thinner portions of the corresponding corrugation  6312  (see  FIG. 41 ), thereby driving the ring plates  632  to move axially and resiliently toward the flange  6311  and decreasing the friction between the side surfaces of the flange  6311  and the ring plates  632  so as to speed up the pivoting movement of the first leaf  611  relative to the second leaf  612 . When the first leaf  611  is further pivoted relative to the second leaf  612  from the 45-degree angular position, each of the protrusions  6321  of the ring plates  632  slides on the corresponding corrugation  6312  to abut against another thicker portion of the corresponding corrugation  6312 , thereby driving the ring plates  632  to move axially away from the flange  6311  to compress the resilient members  633  and increasing the friction between the side surfaces of the flange  6311  and the ring plates  632  so as to slow down the pivoting movement of the first leaf  611  relative to the second leaf  612 . Therefore, the speed of the pivoting movement of the first leaf  611  relative to the second leaf  612  can be automatically adjusted. 
     As shown in  FIGS. 42 and 43 , the eighth preferred embodiment of the hinge device  700  according to the invention has a structure similar to that of the seventh preferred embodiment. The main difference between this embodiment and the previous embodiment resides in the configuration of the friction-providing unit. In this embodiment, the friction-providing unit  730  includes a flange  7311 , a pair of ring plates  732 , and a pair of resilient members  733 . Each of the side surfaces of the flange  7311  is formed with a pair of protrusions  7312 . The ring plates  732  are sleeved rotatably on the shaft  731 . Each of the ring plates  732  has a side plate surface formed with a plurality of corrugations  7321 , each of which is rotatable to contact a corresponding one of the protrusions  7312  in a corresponding one of the side surfaces of the flange  7311 . 
     When the first leaf (not shown) is pivoted from the zero-degree angular position (see  FIG. 42 ) to the 45-degree angular position (see  FIG. 44 ) relative to the second leaf (not shown), the shaft  731  and the flange  7311  are rotated relative to the ring plates  732  to decrease the friction between the side surfaces of the flange  7311  and the ring plates  732  in the same manner as the previous embodiment. Likewise, when the first leaf are further pivoted relative to the second leaf, the shaft  731  and the flange  7311  is further rotated relative to the ring plates  732  from the 45-degree angular position to increase the friction between the side surfaces of the flange  7311  and the ring plates  732  in the same manner as the previous embodiment. 
     Referring to  FIGS. 45 to 48 , the ninth preferred embodiment of the hinge device  800  according to the invention has a structure similar to that of the sixth preferred embodiment. The main difference between this embodiment and the sixth preferred embodiment resides in the following. In this embodiment, the hinge unit  810  includes first and leaves  811 ,  812 , and a knuckle unit  815 . The knuckle unit  815  includes a pair of first knuckles  8151  provided to the first leaf  811 , and a pair of second knuckles  8152  provided to the second leaf  812 . The knuckle unit  815  has an inner surrounding surface unit defining a channel unit  818  therein. In this embodiment, a portion of the channel unit  818  that is within one of the first knuckles  8151  is an engaging channel portion  8111 . A portion of the inner surrounding surface unit that corresponds to one of the second knuckles  8152  is formed with a pair of slide grooves  8121 , each of which extends parallel to the axis (L 5 ). The shaft  831  of the torque-adjusting unit  800  extends in the channel unit  818  along the axis (L 5 ), and includes a cam member  8311  sleeved securely thereon. The cam member  8311  has an engaging portion  8312  inserted fittingly into the engaging channel portion  8111  such that the shaft  831  is coupled co-rotatably to the first leaf  811 , and is formed with a pair of angularly equidistant first spiral surfaces  8313  opposite to the engaging portion  8312  along the axis (L 5 ). The friction-providing unit  830  includes a cam component  832 , an abutment component  835 , and a resilient member  822 . The cam component  832  is disposed in the channel unit  818  and is sleeved movably on the shaft  831 . The cam component  832  is formed with a pair of slide ribs  8322  protruding therefrom, extending parallel to the axis (L 5 ), and engaging respectively and slidably the slide grooves  8121 , such that the cam component  832  is axially slidable relative to the one of the second knuckles  8152 , and is not permitted to rotate relative to the one of the second knuckles  8152 . The cam component  832  is formed with a pair of second spiral surfaces  8321  contacting slidably and respectively the first spiral surfaces  8313 . The abutment component  835  is disposed in the channel unit  818  and is coupled co-rotatably to the first leaf  811 . The resilient member  822  has opposite ends abutting resiliently and respectively against the cam component  832  and the abutment component  835 . When the first leaf  811  is pivoted relative to the second leaf  812 , the first knuckles  8151  are rotatable relative to the second knuckles  8152 , and the shaft  831  is rotated to drive the cam component  832  to move toward the abutment component  835  along the axis (L 5 ) via sliding movement of the first and second spiral surfaces  8313 ,  8321  on each other, thereby compressing the resilient member  822  and increasing friction between the resilient member  822  and the abutment component  835  so as to slow down the pivoting movement of the first leaf  811  relative to the second leaf  812 . 
     As shown in  FIGS. 49 to 52 , the tenth preferred embodiment of the hinge device  900  according to the present invention has a structure similar to that of the sixth preferred embodiment. In this embodiment, the knuckle unit  915  of the hinge unit  910  has an inner surrounding surface unit  919  defining a channel unit  918  therein. A portion of the channel unit  918  is an elliptical channel portion  913 . The friction-providing unit  930  includes a rod member  931 , and a pair of friction-providing blocks  932  that are disposed movably and respectively at diametrically opposite sides of the rod member  931 , and that are biased resiliently and outwardly to move into frictional contact with the inner surrounding surface unit  919 . During the pivoting movement of the first leaf  911  relative to the second leaf  912 , angular orientation of the rod member  931  relative to the elliptical channel portion  913  varies to result in a change of friction between the friction-providing blocks  932  and the inner surrounding surface unit  919  in the same manner as the sixth preferred embodiment, thereby automatically adjusting the speed of the pivoting movement of the first leaf  911  relative to the second leaf  912 . 
     The main difference between this embodiment and the sixth preferred embodiment resides in the following. The rod member  931  has a threaded section  9311  formed at a longitudinal end thereof that is opposite to the shaft  940 . The friction-providing unit  930  further includes a threaded component  933  and a driven member  934 . The threaded component  933  has an end that is formed with a threaded hole  9331  for engaging threadedly the threaded section  9311  of the rod member  931 , and an opposite end that is formed with a hexagonal hole  9332 . The driven member  934  has one end extending through the hexagonal hole  9332  and engaging threadably the threaded component  933 . By removing the driven member  934  and inserting a hand tool into the hexagonal hole  9332  in the threaded component  933 , the threaded component  933  is operable to move axially together with the rod member  931  relative to the friction-providing blocks  932 , thereby adjusting friction between the friction-providing blocks  932  and the inner surrounding surface unit  919 . 
     While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements.