A hinge unit is formed of a case with an inside wall, a rotating cam freely rotatably accommodated inside the case, a slide cam accommodated inside the case such that the slide cam is prevented from rotating relative to the case and is moved freely in an axial direction along the inside wall of the case, and an urging device accommodated inside the case to urge the slide cam toward the rotating cam. Cam surfaces are formed on the rotating cam and the slide cam to abut against each other. The cam surfaces has a contact range from a full-surface contact to a partial contact according to a relative rotational angle of the slide cam and rotating cam.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a hinge unit which regulates the angle of rotation, and a hinge structure which uses this hinge unit to support a first box-form body and a second box-form body so that these box-form bodies can rotate relative to each other. 
     FIGS. 11 and 12 show a hinge unit  100  which is used in a foldable portable telephone. Here, a cylindrical first cam body  104  and second cam body  106  are fit over a shaft  102 , so that these cam bodies can rotate relative to the shaft  102 . 
     The first cam body  104  and second cam body  106  have the same shape, and the cam surface  104 A of the first cam body  104  and a cam surface  106 A of the second cam body  106  contact each other over their entire surfaces in a state that the cam bodies are rotated 90° about the shaft  102 . 
     Meanwhile, a flange part  102 A is formed on one end of the shaft  102 , so that the first cam body  104  is prevented from slipping off. Furthermore, an E-ring  108  is fit over the other end of the shaft  102 . 
     A compression coil spring  110  is mounted between the E-ring  108  and the second cam body  106 , so that the second cam body  106  is urged toward the first cam body  104 . Accordingly, the second cam body  106  contacts the first cam body  104  or moves away from the first cam body  104  while sliding over the shaft  102  in accordance with the opening angle of the second box-form body  112 , thus applying an opening force to the second box-form body  112 . 
     Thus, a tentatively assembled hinge unit  100  is constructed by the shaft  102 , first cam body  104 , second cam body  106  and compression coil spring  110 . However, since various parts of this hinge unit  100  are exposed, the hinge units  100  may become entangled with each other when a plurality of hinge units  100  is packaged and shipped, so that handling is difficult. 
     In view of the above facts, an object of the present invention is to provide a hinge unit in which there is no entanglement of a plurality of packaged hinge units with each other even if the first box-form body and second box-form body are not attached, so that handling is easy. 
     Another object of the invention is to provide a hinge unit as stated above, wherein the attachment of the above mentioned hinge unit to the first box-form body and second box-form body is easy. 
     Further objects and advantages of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     In a first aspect of the invention, a rotating cam and a slide cam are accommodated in a case, and the rotating cam can rotate relative to the case. Meanwhile, the slide cam is prevented from rotating relative to the case, but can move in the axial direction along the inside wall of the case. Furthermore, the slide cam is urged toward the rotating cam by driving means accommodated in the case. 
     Here, cam surfaces are formed on the abutting surfaces of the slide cam and rotating cam, and these cam surfaces make contact with each other or move away from each other according to the relative rotational angle of the slide cam and rotating cam, so that the cam surfaces has a contact configuration ranging from a full-surface contact to a partial contact. 
     Thus, by the movement of the slide cam along the inside wall of the case, even if no shaft is used, the axis does not shift when the slide cam moves. Specifically, since the case is provided with the function of a shaft, an increase in the number of parts of the hinge unit can be prevented. 
     Furthermore, since the slide cam, rotating cam and driving means are accommodated inside the case, there is no exposure of these various parts. As a result, there is no entanglement of a plurality of packaged hinge units with each other, so that handling is easy. 
     Furthermore, in this hinge unit, if the case is held and a torque is applied to the rotating cam, the slide cam and rotating cam can be rotated relative to each other. Accordingly, mechanical numerical values, such as the required torque, etc., can be determined. Consequently, torque can be controlled for the hinge unit, so that there is little variation in the product. 
     Considering a case in which this hinge unit is used, for example, with the case attached to a shaft part on the main body side and the rotating cam connected to a shaft part on the cover side, the rotating cam rotates relative to the case when the cover is opened in the opening direction from a closed state, so that the slide cam moves along the axis of the case in the direction in which the slide cam is separated from the rotating cam by the action of the cam surfaces, thus causing the contact configuration of the cam surfaces to reach a partial contact. 
     When the cover is further opened from this stage, the cam surface of the rotating cam rides over the peak parts of the cam surface of the slide cam, so that the slide cam is caused to move toward the rotating cam by the driving force of the driving means. This moving force is converted by the cam surfaces into a force that rotates the cover via the rotating cam. 
     In a second aspect of the invention, the slide cam contacts inside the case. As a result, shifting of the axis of the slide cam is prevented even more securely. 
     In a third aspect of the invention, a connecting part is formed on the rotating cam, and this connecting part protrudes to the outside from the box-form case. By thus causing a connecting part to protrude from the case, it is possible to apply torque to the rotating cam without any particular need to screw a connecting tool, etc., into the rotating cam. 
     Meanwhile, a square guide plate is molded as an integral part of the slide cam, and this guide plate can slide along the inside wall of the case. By thus forming the case in a box shape and forming the square guide plate on the slide cam, it is possible to prevent rotation of the slide cam by means of a simple structure. 
     In a fourth aspect of the invention, the connecting part is formed in the shape of a square column. Accordingly, since the connecting part is prevented from rotating with respect to the accommodating part merely by forming the accommodating part with an angular shape, there is no need to use a complex shape as in conventional device, so that working costs can be reduced. 
     In a fifth aspect of the invention, the diameter of the circumferential wall of the aforementioned slide cam is the same as the width of the aforementioned guide plate. Accordingly, not only the side surfaces of the guide plate, but also the circumferential wall surfaces of the slide cam, slide along the inside wall of the case, so that the sliding contact area with the inside wall of the case is increased. Consequently, the slide cam can move without any shift in the axis of the slide cam. 
     In a sixth aspect of the invention, the aforementioned cam surface of the slide cam includes peak parts and valley parts, and the peak parts and valley parts are disposed at 90-degree intervals. Furthermore, the corner parts of the aforementioned guide plate are positioned in the vicinity of straight lines that connect the axial center of the slide cam with the valley parts as seen in a plan view. 
     Since the parts that slide along the inside wall of the case are the circumferential wall of the slide cam and the side surfaces of the guide plate, the contact area of the inside wall of the case relative to the circumferential wall of the slide cam and side surfaces of the guide plate can be large in order to prevent any shift in the axis of the slide cam. 
     Accordingly, in case where the side surfaces of the guide plate are positioned in the vicinity of the straight line that connects the axis of the slide cam and the valley parts of the cam surface, the valley parts and peak parts of the cam surface are positioned substantially at the centers of the side surfaces of the guide plate. 
     In this case, the length that slides along the inside wall of the case at the approximate centers of the side surfaces of the guide plate becomes equal to the thickness of the guide plate on the sides of the valley parts of the cam surface. Meanwhile, on the side of the peak part of the cam surface, the length that slides along the inside wall of the case is a length produced by adding the height of the peak part to the thickness of the guide plate. 
     Since the length that slides along the inside wall of the case at the approximate center of the side surface of the guide plate varies between the peak part side and valley part side, the contact area between the inside wall of the case and the circumferential wall of the slide cam and side surfaces of the guide plate varies, so that there is a danger that the axis may shift in some cases where the slide cam moves. 
     However, in case the corner parts of the guide plate are disposed in the vicinity of the straight line that connects the axis of the slide cam with the valley parts as seen in a plan view, the lengths that slide along the inside wall of the case at the approximately centers of the side surfaces of the guide plate are all the same. 
     As a result, the contact area between the inside wall of the case and the circumferential wall of the slide cam and side surfaces of the guide plate remains more or less the same. consequently, the slide cam moves more stably, so that there is no danger that the axis of the slide cam will shift. 
     In a seventh aspect of the invention, closing parts extend from the case, and are bent so that these closing parts prevent the slide cam from ejection of the case. Thus, since the slide cam can be prevented from ejection merely by bending these closing parts, the working characteristics are good. 
     In an eighth aspect of the invention, cut-out parts are formed at the base parts of the closing parts, and these cut-out parts determine the bending positions when the closing parts are bent. Thus, the bending of the closing parts is facilitated by the formation of cut-out parts at the base parts of the closing parts. Furthermore, since the bending positions are determined by the cut-out parts, protrusion of the bending position from the plane of the peripheral edge parts of the case can be prevented.. 
     In a ninth aspect of the invention, a plurality of driving means is used. As a result, since the area contacting the slide cam is increased as compared to a case in which a single driving means is used, the slide cam can move smoothly with a good balance. Furthermore, as a result of the use of a plurality of driving means, fine adjustment of the driving force is possible. 
     In a tenth aspect of the invention, the rotating cam is connected to a shaft part installed in a first box-form body, the case is fastened to a shaft part installed in a second box-form body, and the first box-form body and second box-form body can rotate relative to each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view showing a main body and a cover of a portable telephone equipped with a hinge unit of the present invention; 
     FIG. 2 is an exploded perspective view of the hinge unit of the present invention; 
     FIG.  3 (A) is a perspective vies of a slide cam used in the hinge unit of the present invention; and 
     FIG.  3 (B) is a plan view thereof; 
     FIG.  4 (A) is a perspective view of a slide cam shown for comparison with FIG.  3 (A); and 
     FIG.  4 (B) is a plan view thereof; 
     FIG. 5 is an explanatory sectional view illustrating a case in which the slide cam shown in FIGS.  4 (A) and  4 (B) is used for showing a state in which the slide cam is tilted; 
     FIG. 6 is an explanatory sectional view illustrating a case in which the slide cam shown in FIG.  4 (A) is used for showing a state in which a gap is formed between the slide cam and the rotating cam; 
     FIG. 7 is an explanatory sectional view illustrating a case in which the slide cam shown in FIG.  4 (A) is used for showing a state in which the slide cam is tilted; 
     FIG.  8 (A) is a side view of the hinge unit; 
     FIG.  8 (B) is a side view showing a state in which the cover of the portable telephone is closed; and 
     FIG.  8 (C) is a view showing a state of engagement of the cam surfaces; 
     FIG.  9 (A) is a side view of the hinge unit of the present invention; 
     FIG.  9 (B) is a side view showing a state in which the cover of the portable telephone is opened to an intermediate position; and 
     FIG.  9 (C) is a view showing a state of engagement of the cam surfaces; 
     FIG.  10 (A) is a side view of the hinge unit of the present invention; 
     FIG.  10 (B) is a side view showing a state in which the cover of the portable telephone is completely opened; and 
     FIG.  10 (C) is a view showing a state of engagement of the cam surfaces; 
     FIG. 11 is a partial sectional view which shows a conventional hinge structure; and 
     FIG. 12 is an exploded perspective view of a conventional hinge structure. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a portable telephone  12  using a hinge unit  10  (see FIG. 2) of the present invention. 
     A substantially square columnar supporting body  16  is disposed on an end portion of a main body or first box-form body  14  of this portable telephone  12 . Both sides and a dial part  18  of this supporting body  16  are cut away so that when a cover or second box-form body  20  is closed, the outside surface of the main body  14  and the cover  20  become co-planar. 
     Furthermore, a hinge unit  10  is attached to the supporting body or shaft part  16  and bifurcated, substantially cylindrical shaft bodies or shaft parts  22  which protrude from the cover  20 . The shaft parts  22  clamp both end parts of the supporting body  16 . In this way, the shaft bodies  22  are supported on the supporting body  16  so that the shaft bodies  22  can rotate. 
     As is shown in FIG. 2, the case  24  has a box shape, and a round hole  24 B is formed in the center of the bottom part of the case  24 . A connecting part  32  formed on a rotating cam  30  (described later) can protrude into this round hole  24 B. 
     Here, the rotating cam  30  has a substantially cylindrical shape, and is accommodated inside the case  24 , so that the rotating cam  30  can rotate about the shaft part of the case  24 . A cam surface  34  (described later) is formed on one end of this rotating cam  30 , and a square columnar connecting part  32  protrudes from the other end of this rotating cam  30 . 
     This connecting part  32  can engage the accommodating part  36  shown in FIG.  1 . The accommodating part  36  is recessed to face the shaft part  22  of the cover  20 , and has a square shape that allows engagement of the connecting part  32 . 
     Since the connecting part  32  and accommodating part  36  have square shapes, the rotating cam  30  is prevented via the connecting part  32  from rotating relative to the accommodating part  36 , as a result of the engagement of the connecting part  32  inside the accommodating part  36 . Since the rotating cam and accommodating part do not have complicated shapes as in a conventional device, the working costs can be reduced. 
     Here, an accommodating part  37  that allows the fastening of the case  24  is recessed in the supporting body  16  to face the accommodating part  36 , and the case  24  is fastened to the supporting body  16 . Accordingly, when the cover  20  is rotated in a state in which the rotating cam  30  is connected to the shaft body  22 , the rotating cam  30  rotates through the inside of the case  24  via the shaft body  22 . 
     Here, furthermore, the connecting part  32  is formed with a square columnar shape, and the accommodating part  36  is formed with a square shape that allows engagement of the connecting part  32 . However, it is sufficient if rotation of the connecting part  32  relative to the accommodating part  36  is prevented when the connecting part  32  is engaged with the accommodating part  36 . Accordingly, the present invention is not limited to such shapes, and it would also be possible to form the connecting part with a hexagonal columnar shape, and to form the accommodating part with a hexagonal shape that corresponds to the shape of the connecting part. 
     Meanwhile, as is shown in FIG.  2  and FIG.  3 (A), a slide cam  38  is accommodated inside the case  24  to face the rotating cam  30 . This slide cam  38  is constructed with a cylindrical cam part  40  and a square guide plate  42 , and is formed as an integral unit. 
     This slide cam  38  is prevented from rotating relative to the case  24  by the guide plate  42 . The width of the guide plate  42  is set so that it is slightly smaller than the width of the inside walls of the case  24 , so that the side surfaces of the guide plate  42  can slide along the inside wall of the case  24  and move in the axial direction of the case  24  (described later). 
     A protruding part  44  protrudes from the undersurface of the guide plate  42 , and a small spring  46  can be mounted on this protruding part  44 . One end part of this small spring  46  contacts the guide plate  42 , while the other end contacts the closing parts  26  (described later) after the closing parts  26  have been bent, so that the slide cam  38  is urged toward the rotating cam  30 . 
     Furthermore, as a result of the small spring  46  mounted on the protruding part  44 , shifting of the axis of the small spring  46  is prevented. Furthermore, a large spring  48  is inserted between the small spring  46  and the case  24 , and this large spring  48  contacts the case  24  from the inside. 
     Accordingly, even if the large spring  48  expands or contracts, there is no shifting of the axis of the large spring  48 . Like the small spring  46 , the large spring  48  urges the slide cam  38  toward the rotating cam  30 . 
     Thus, as a result of the use of the above mentioned small spring  46  and large spring  48 , the area that contacts the guide plate  42  is increased as compared to a case in which only a single spring is used. Accordingly, the slide cam  38  can move smoothly with a good balance. Furthermore, as a result of the use of a plurality of springs, fine adjustment of the driving force is possible. 
     Meanwhile, a pair of closing parts  26  extends from the peripheral edge  24 A of the open side of the case  24 , and these closing parts  26  can be bent toward the inside of the case  24 . These closing parts  26  have an area that is capable of holding at least the small spring  46 . 
     As a result, when the closing parts  26  are bent toward the inside of the case  24 , the rotating cam  30 , slide cam  38 , small spring  46  and large spring  48  accommodated inside the case  24  are prevented from falling out of the case  24  (see FIG.  8 (A)). Thus, since the slide cam  38  can be prevented from being ejected merely by bending the closing parts  26 , the working characteristics are good. 
     Furthermore, circular-arc-form cut-out parts  28  are formed at the base part of each closing part  26 . These cut-out parts  28  determine the bending positions when the closing parts  26  are bent. As a result, the bending of the closing parts  26  is facilitated. Furthermore, since the bending position is determined by the cut-out parts  28 , protrusion of the bending position from the plane of the peripheral edge  24 A of the case  24  can be prevented. 
     Here, furthermore, the slide cam  38  is prevented from being ejected by means of a pair of closing parts  26 . However, since it is sufficient if the slide cam  38  is prevented from ejection, the present invention is not limited to this arrangement, and a single closing part  26  may also be used. 
     Meanwhile, it is desirable that the contact area between the inside wall of the case  24  and the slide cam  38  is large in order to prevent any shift in the axis of the slide cam  38 . Accordingly, the external diameter of the outer circumferential surface of the cam part  40  is set at the same value as the width of the guide plate  42 , so that the cam part  40  and guide plate  42  are of such a size that these parts make inside contact with the inside walls of the case  24 . 
     As a result, when the slide cam  38  moves along the axial direction of the case  24 , not only the side surfaces of the guide plate  42  but also the outer circumferential surface of the cam part  40  slide along the inside wall of the case  24 . 
     Here, a cam surface  50  (described later) is formed on the cam part  40 , and is disposed to face the cam surface  34 . Peak parts  50 A and valley parts  50 B are disposed on this cam surface  50  at 90-degree intervals, and these peak parts  50 A and valley parts  50 B extend smoothly. 
     For example, in a slide cam  60  in which the side surfaces of the guide plate  42  are positioned in the vicinity of the straight lines that connect the axis of the cam part  40  with the valley parts  50 B of the cam surface  50  as seen in a plan view, i. e. FIGS.  4 (A) and  4 (B), 
     In this case, the length that slides along the inside wall of the case  24  at the approximately centers of the side surfaces of the guide plate  42  is only equal to the thickness t of the guide plate  42  on the sides of the valley parts  50 B of the cam surface  50 . On the other hand, on the sides of the peak parts  50 A of the cam surface  50 , the length that slides along the inside walls of the case  24  is a length obtained by adding the height h of the peak parts  50 A to the thickness t of the guide plate. 
     Accordingly, the length that slides along the inside wall of the case  24  differs between the sides of the peak parts  50 A and the sides of the valley parts  50 B. Consequently, the contact area with the outer circumferential surface of the cam part  40  and the side surfaces of the guide plate  42  differs on the parts of the inside wall of the case  24 . Therefore, for example, when the slide cam  60  moves without the guide plate  42  being driven with a good balance, there is a danger that the axis of the slide cam  60  will shift. 
     In this case, the slide cam  60  tilts as shown in FIG. 5, so that an impact sound is generated between the slide cam  60  and the inside wall of the case  24 . Furthermore, since the slide cam  60  can not move smoothly through the inside of the case  24  in a stable state, the cam surface  50  of the slide cam  60  can not trace the cam surface  34  of the rotating cam  30 , so that gaps may be formed as shown in FIG.  6 . 
     Even in a case where there is a movement from this state into a state in which the cam surface  50  and cam surface  34  contact as shown in FIG. 7, an impact sound is generated between the slide cam  60  and the inside walls of the case  24 , or between the slide cam  60  and the cam  30 . 
     On the other hand, in the case of the slide cam  38  in which the corner parts of the guide plate  42  are disposed in the vicinity of the straight lines that connect the axis of the cam part  40  and the valley parts  50 B as seen in a plan view, i. e., as shown in FIGS.  3 (A) and  3 (B), the length that slides along the inside wall of the case  24  at the approximate centers of the side surfaces of the guide plate  42  is obtained by adding the height H to the thickness t of the guide plate  42 , and this length is the same length on the respective side surfaces. 
     Accordingly, the contact areas of the outer circumferential surfaces of the cam part  40  and the side surfaces of the guide plate  42  are the same on the parts of the inside wall of the case  24 , so that the slide cam  38  can move stably with a good balance, without any shift of the axis of the slide cam  38 . 
     In the present configuration, as a result of the above construction, the slide cam  38  is accommodated while contacting the case  24 . Consequently, there is no shifting of the axis of the slide cam  38 , as in the conventional device, when the slide cam  38  moves, even if no shaft is used. Specifically, as a result of the case  24  provided with the function of a shaft, an increase in the number of parts of the hinge unit can be prevented. 
     Here, furthermore, shifting of the axis of the slide cam  38  is prevented by causing the slide cam  38  to contact the case  24  from the inside. However, since it is sufficient if no gap that generates an impact sound, etc., is formed between the slide cam  38  and the inside wall of the case  24  when the slide cam  38  moves, it is not absolutely necessary that the slide cam  38  contacts the case  24  from the inside. 
     Furthermore, since the rotating cam  30 , slide cam  38 , small spring  46  and large spring  48  are accommodated inside the case  24 , these respective parts are not exposed. As a result, there is no mutual entanglement of a plurality of packaged hinge units  10 , so that handling is easy. 
     Furthermore, in the hinge unit  10  of the present configuration, if the case  24  is held and a torque is applied to the rotating cam  30 , the slide cam  38  and rotating cam  30  can rotate relative to each other even if the hinge unit  10  is not attached to the main body  14  and cover  20 . Accordingly, torque control of the hinge unit  10  is possible, so that there is little variation in the product. 
     Here, the operation of the slide cam  38  and rotating cam  30  will be described. 
     The cam surface  50  which can contact the cam surface  34  of the rotating cam  30  is recessed in the slide cam  38 . In a state in which the cover  20  is closed, as is shown in FIGS.  8 (A),  8 (B) and  8 (C), the peak parts  50 A of the cam surface  50  of the slide cam  38  and the valley parts  34 B of the cam surface  34  of the rotating cam  30  do not engage, so that the cam surfaces  34  and  50  make no contact over their entire surfaces. 
     Specifically, as a result of the abutment of the cam surface  50  of the slide cam  38  and the cam surface  34  of the rotating cam  30 , the slide cam  38  which is urged by the small spring  46  and the large spring  48  is loaded with a force in the direction indicated by the arrow F due to the axial urging or driving force received from the small spring  46  and large spring  48 . 
     As a result, the axial driving force of the small spring  46  and large spring  48  is converted by the rotating cam  30  into a rotational force that tends to cause rotation in the direction that closes the cover  20 . Accordingly, the cover  20  can cover the main body  14  without any looseness, and will not open even if the cover  20  is turned upside down. 
     Next, as is shown in FIGS.  9 (A),  9 (B) and  9 (C), when the cover  20  is opened in the direction indicated by the arrow M against the driving force of the small spring  46  and large spring  48 , the slide cam  38  is pushed against the rotating cam  30  as a result of the abutment of the inclined surfaces of the cam surface  50  and the peak parts  34 A of the cam surface  34 , so that the slide cam  38  is pushed back into the interior of the case  24 . Then, the cover  20  is opened to a position where the peak parts  34 A of the cam surface  34  of the rotating cam  30  and the peak parts  50 A of the cam surface  50  of the slide cam  38  abut against each other. 
     Here, the slide cam  38  and rotating cam  30  are molded from a synthetic resin, and a clicking feeling is obtained in the position where the peak parts  34 A of the cam surface  34  of the rotating cam  30  and the peak parts  50 A of the cam surface  50  of the slide cam  38  abut against each other. Furthermore, the peak parts  34 A of the cam surface  34  slide over the inclined surfaces toward the valley parts  50 B of the cam surface  50 , so that the cover  20  naturally opens in the direction M. 
     Specifically, as a result of the abutment of the cam surface  50  of the slide cam  38  and the cam surface  34  of the rotating cam  30 , the slide cam  38  which is urged by the small spring  46  and the large spring  48  is loaded with a force in the direction indicated by the arrow M due to the axial driving force received from the small spring  46  and large spring  48 . 
     As a result, the axial driving force of the small spring  46  and large spring  48  is converted by the rotating cam  30  into a rotational force that tends to cause rotation in the direction that opens the cover  20 . When the cam surface  50  of the slide cam  38  and the cam surface  34  of the rotating cam  30  make contact over their entire surfaces as shown in FIGS.  10 (A),  10 (B) and  10 (C), the cover  20  stops. In the present configuration, the opening angle of the cover  20  in this state is set at 135°. 
     If an attempt is made to open the cover  20  even further from this stage, the valley parts  34 B of the cam surface  34  of the rotating cam  30  ride over the peak parts  50 A of the cam surface  50  of the slide cam  38 . If the rotational force applied to the cover is released in this state, the slide cam  38  moves toward the rotating cam  30  by the driving force of the small spring  46  and large spring  48 . 
     The force of this movement is converted by the cam surfaces  34  and  50  into a force that rotates the cover  20  via the rotating cam  30 , so that the cover is returned to a state in which the opening angle theta of the cover  20  is 135°. 
     Thus, as a result of the cam surfaces  34  and  50  respectively formed on the abutting surfaces of the slide cam  38  and rotating cam  30 , the hinge unit  10  can be designed as a compact unit. Furthermore, the opening angle of the cover  20  can be adjusted by varying the shape of the cam surface  34 . 
     Furthermore, in the present configuration, the slide cam  38  contacts the inside wall of the case  24  from the inside. Accordingly, although a resistance to rotation is applied to the shaft body  22  (see FIG. 1) attached to the hinge unit  10 , this resistance to rotation is minimized by making the sliding surface of the inside wall of the case  24  and the slide cam  38  smooth surfaces, so that the mutual coefficient of friction is reduced. 
     Here, furthermore, the case  24  was installed on the side of the main body  14 , and the connecting part  32  of the rotating cam  30  was connected to the side of the cover  20 . However, it goes without saying that the reverse arrangement would also be possible. 
     Furthermore, in the present configuration, the connecting part  32  protrudes from the rotating cam  30 . However, since it is sufficient if the rotating cam  30  and shaft body  22  can be connected, it would also be possible, for example, to install a protruding part on the side of the shaft body and form a recess with which this protruding part can engage in the rotating cam, and to connect the rotating cam  30  and shaft body  22  by causing this recess to engage the protruding part. 
     Furthermore, a portable telephone  12  using a cover  20  capable of rotating relative to a main body  14  has been described above. However, since the product to which the present invention is applied may be any product that uses a hinge unit  10 , the same effect as that of the present invention can also be obtained in a folding type portable telephone. 
     Furthermore, the present invention can be used not only in portable telephones, but also in other devices in which the opening angle is determined, such as the covers of an AV equipment, etc. 
     The present invention is constructed as described above. Accordingly, in the first, second and tenth aspects of the invention, there is no shift of the axis when the slide cam moves, even if no shaft is used. Specifically, as a result of the case provided with the function of a shaft, an increase in the number of parts of the hinge unit is prevented. Furthermore, since the slide cam, rotating cam and driving means are accommodated inside a case, there is no exposure of these respective parts. 
     Accordingly, there is no mutual entanglement of a plurality of packaged hinge units, so that handling is easy. Furthermore, in this hinge unit, if a torque is applied to the rotating cam while the case is held, the slide cam and rotating cam can rotate relative to each other, so that mechanical numerical values such as the required torque, etc., can be determined. Accordingly, the torque control of the hinge unit is possible, so that there is little variation in the product. 
     In the third aspect of the invention, since the connecting part protrudes from the case, a torque can be applied to the rotating cam without screwing any particular connecting tool, etc., into the rotating cam. Furthermore, since the case is formed in a box shape and a square guide plate is formed on the slide cam, rotation of the slide cam can be prevented by means of a simple structure. 
     In the fourth aspect of the invention, rotation of the connecting part relative to the accommodating part is prevented merely by forming the accommodating part with a square shape. Accordingly, there is no need to form a complicated shape as in conventional devices, so that working costs are reduced. 
     In the fifth aspect of the invention, not only the side surfaces of the guide plate but also the circumferential wall surface of the slide cam slides along the inside wall of the case, so that the sliding area with the inside wall of the case is increased. Accordingly, the slide cam can move stably without any shifting of the axis of the slide cam. 
     In the sixth aspect of the invention, the contact areas of the inside wall of the case with respect to the circumferential wall of the slide cam and the side surfaces of the guide plate are substantially the same. Accordingly, the slide cam can move stably, and there is no shifting of the axis of the slide cam. 
     In the seventh aspect of the invention, the slide cam can be prevented from protrusion merely by bending the closing parts. Accordingly, the working characteristics are good. In the eighth aspect of the invention, the closing parts are made more easily bendable. Furthermore, since the bending position is determined by the cut-out parts, protrusion at the bending position from the plane of the edge parts of the case can be prevented. 
     In the ninth aspect of the invention, the area that contacts the slide cam is increased as compared to a case in which only single driving means is used. Accordingly, the slide cam can move smoothly with a good balance. Furthermore, as a result of the use of a plurality of driving means, fine adjustment of the driving force is possible. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.