Patent Publication Number: US-2007102250-A1

Title: Rotary damper

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This is a divisional application of U.S. patent application Ser. No. 10/950,573 filed on Sep. 28, 2004. 
    
    
     BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT  
      The invention relates to a rotary damper for damping a rotation of a driven gear engaging a gear or a rack.  
      A rotary damper is formed of a housing; a viscous fluid filled inside the housing; a rotor disposed in the housing and having a shaft part partially protruding from the housing and a resistance part provided on the shaft part for moving within the viscous fluid inside the housing; and a seal member for sealing between the shaft part of the rotor and the housing to prevent leakage of the viscous fluid. A driven gear is attached to the shaft part protruding from the housing (refer to Japanese Patent Publication (Kokai) No. 04-34015).  
      A conventional rotary damper has a resistance part having an elliptical shape, so that air mixed into the housing during assembly is not allowed to be positioned between the resistance part of a rotor, i.e. a torque generating part, and a bottom surface or ceiling surface of the housing. However, because the rotor rotates in both directions, the air mixed into the housing generates a noise when the air moves over the resistance part to the opposite side of the resistance part. The noise generated when the air mixed into the housing moves over the resistance part is believed to be a bursting sound caused by the air mixed into the housing being compressed by moving up the resistance part and then being released suddenly when moving over the resistance part. Such a noise tends to happen more frequently when the viscous fluid has a higher viscosity, or when a distance between the rotor and the housing is narrower.  
      In view of the problem described above, an object of the invention is to provide a rotary damper, in which air mixed into a housing and compressed by moving up on a resistance part is gradually released during assembly, so that it is possible to prevent a noise caused by the air mixed into a housing even when the rotor rotates in both directions.  
      Further objects and advantages of the invention will be apparent from the following description of the invention.  
     SUMMARY OF THE INVENTION  
      In order to attain the objects described above, according to a first aspect of the present invention, a rotary damper includes a housing; a viscous fluid filled in the housing; a rotor disposed inside the housing and having a shaft part partially protruding from the housing and a resistance part provided on the shaft part for moving in the viscous fluid inside the housing; and a seal member for sealing between the shaft part and the housing to prevent leakage of the viscous fluid. The rotary damper further includes a first sloping part provided on an upstream side of the rotating resistance part and having a distance relative to an inner surface of the housing gradually decreasing toward a downstream side; and a second sloping part provided on a downstream side of the rotating resistance part and having a distance relative to the inner surface of the housing gradually increasing toward a downstream side.  
      According to a second aspect of the invention, in the rotary damper in the first aspect, the first sloping part and second sloping part are provided on an outer perimeter part of the resistance part.  
      According to a third aspect of the invention, in the rotary damper in the first aspect, the first sloping part and second sloping part are provided on an inner perimeter surface of the housing.  
      According to a fourth aspect of the invention, in the rotary damper in one of the first to third aspects, a plurality of the first sloping parts and second sloping parts are provided.  
      In the first aspect of the invention, the rotary damper includes the first sloping part provided on an upstream side of the rotating resistance part and having a distance relative to the inner surface of the housing gradually decreasing toward a downstream side; and the second sloping part provided on a downstream side of the rotating resistance part and having a distance relative to the inner surface of the housing gradually increasing toward a downstream side. Even if air mixed into the housing flows into between the inner surface of the housing and the first sloping part during assembly, the air is gradually compressed and then is gradually released. Accordingly, it is possible to prevent generation of a noise caused by the air mixed into the housing even when the rotor rotates in both directions.  
      In the second aspect of the invention, the first sloping part and second sloping part are provided on the outer perimeter part of the resistance part, where a negative pressure tends to be generated most easily when the rotor rotates. In the third aspect of the invention, the first sloping part and second sloping part are provided on the inner perimeter surface of the housing. Accordingly, it is possible to effectively prevent generation of a noise caused by the air mixed into the housing.  
      In the fourth aspect of the invention, a plurality of the first sloping parts and second sloping parts are provided. Accordingly, it is possible to adjust torque within a wide range and increase the torque regardless of a position of the air mixed into the housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view of a rotary damper according to a first embodiment of the invention;  
       FIG. 2  is a perspective view of a rotor shown in  FIG. 1 ;  
       FIG. 3  is a perspective view of a rotor constituting a rotary damper according to a second embodiment of the invention;  
       FIG. 4  is a sectional view of a radial pole taken along line  4 - 4  in  FIG. 3 ;  
       FIG. 5  is a sectional view of a rotor constituting a rotary damper according to a third embodiment of the invention;  
       FIG. 6  is a perspective view of a rotor constituting a rotary damper according to a fourth embodiment of the invention;  
       FIG. 7  is a sectional view taken along line  7 - 7  in  FIG. 6 ;  
       FIG. 8  is a perspective view of a rotor constituting a rotary damper according to a fifth embodiment of the invention;  
       FIG. 9  is a perspective view of a rotor constituting a rotary damper according to a sixth embodiment of the invention;  
       FIG. 10  is a plan view of a rotor constituting a rotary damper according to a seventh embodiment of the invention; and  
       FIG. 11  is a perspective view of a rotor constituting a rotary damper according to an eighth embodiment of the invention.  
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Hereunder, embodiments of the invention will be explained with reference to the accompanying drawings.  FIG. 1  is a sectional view of a rotary damper according to a first embodiment of the invention, and  FIG. 2  is a perspective view of the rotor shown in  FIG. 1 .  
      As shown in  FIG. 1 , a rotary damper D includes a case  11  made of a synthetic resin; silicone oil  21  as a viscous fluid filled inside the case  11 ; and a rotor  31  made of a synthetic resin and disposed inside the case  11 . The rotor  31  has a shaft part  32  partially protruding from the case  11 , and resistance parts  36  provided on the shaft part  32  for moving within the silicone oil  21  inside the case  11 . The rotary damper D further includes a cap  61  made of a synthetic resin for closing an opening of the case  11  and having a through-hole  62  for inserting the shaft part  32  of the rotor  31 ; an O-ring  71  as a seal member for sealing between this cap  61  and the shaft part  32  of the rotor  31  to prevent leakage of the silicone oil  21 ; and a driven gear  81  made of a synthetic resin and attached to the shaft part  32  of the rotor  31  projecting from the cap  61 . A housing is formed of the case  11  and the cap  61 .  
      The case  11  is formed of a case main body  12  having a bottom part  13  with a circular planar shape and a cylindrical wall part  14  extending along an outside edge of the bottom part  13 ; a cylindrical bearing part  16  provided in the center of an inner surface  13   a  of the bottom part  13 ; and attachment flanges  17  provided on an outer perimeter of the case body  12  in a radial direction at, for example, a 180-degree interval, and having an attachment hole  18 .  
      An encircling thin protruding cylindrical part  14   b  protrudes from an upper side of the cylindrical wall part  14 , and has an inner surface extending from an inner perimeter surface  14   a  of the cylindrical wall part  14 . A receiving part  15  is formed inside the case main body  12  for retaining the silicone oil  21 , and corresponds to a part below the thin protruding cylindrical part  14   b.    
      The rotor  31  is formed of the shaft part  32  with a cylindrical shape, and a plurality of, in the embodiment two provided at a 180-degree interval, resistance parts  36  extending from the shaft part  32  outwardly in a radial direction. A recess  33  with a cylindrical shape is formed on a bottom surface of the shaft part  32  for engaging a bearing part  16  of the case  11  to be rotatable. The shaft part  32  is also provided with I-cut sections  34  at a part thereof protruding from the cap  61 , and horizontal coupling grooves  35  on a plane part (perpendicular plane) of each of the I-cut sections, respectively.  
      As shown in  FIG. 2 , each of the resistance part  36  is formed of a radial flat plate  37  extending horizontally and radially from the shaft part  32 , and an arc-shaped plate  38  provided on an outer perimeter edge of the radial flat plate  37  in the circumferential direction and facing an inner surface of the case  11 , i.e. the inner perimeter surface  14   a  of the cylindrical wall part  14 . Further, sloping parts  39 A and  39 B are provided on the arc-shaped plate  38  at both ends thereof in the horizontal direction, as shown in  FIG. 2 , so that a distance gradually decreases toward a center side.  
      When the rotor  31  rotates in a clockwise direction in  FIG. 2 , the sloping parts  39 A become a first sloping part positioned at an upstream side of the resistance parts  36 , where a distance relative to the inner perimeter surface  14   a  of the cylindrical wall part  14  gradually decreases toward a downstream side, and the sloping parts  39 B become a second sloping part positioned at a downstream side of the resistance parts  36 , where a distance relative to the inner perimeter surface  14   a  of the cylindrical wall part  14  gradually increases toward a downstream side. Also, when the rotor  31  rotates in the counterclockwise direction in  FIG. 2 , the sloping parts  39 B become the first sloping part, and the sloping parts  39 A become the second sloping part.  
      A through-hole  62  is provided at the center of the above-mentioned cap  61  for inserting the shaft part  32  of the rotor  31 . An enlarged diameter section  63  having a cylindrically cut out portion reaching a bottom end is provided on a lower side of the through-hole  62  for receiving an O-ring  71 . An encircling coupling recess  64  is provided around an outside edge of the cap  61  at a lower side for engaging the thin protruding cylindrical part  14   b  of the case main body  12 . Reference numeral  61   a  indicates an inner surface (lower surface) of the cap  61 . An I-cut attachment hole  82  is provided at a center of the driven gear  81 , and a coupling band  83  is provided on a flat planar part of the attachment hole  82  for engaging the coupling groove  35  provided on the shaft part  32  of the rotor  31 .  
      A process of assembling the rotary damper D will be explained next. First, the shaft part  32  of the rotor  31  is inserted into the O-ring  71 , and silicone oil  21  is applied to the recess  33  and the resistance parts  36 . Then, a part of the shaft part  32  and the resistance parts  36  are installed inside the receiving part  15  so that the bearing part  16  of the case  11  is fitted into the recess  33 . After a suitable quantity of silicone oil  21  is filled into the receiving part  15 , the thin protruding cylindrical part  14   b  is fitted into the coupling recess  64  of the cap  61  while the shaft part  32  is inserted into the through-hole  62 , and the opening of the case  11  is closed with the cap  61 .  
      When the opening of the case  11  is closed with the cap  61 , almost all of the air inside the thin protruding cylindrical part  14   b  is discharged to the outside of the case  11 . The thin protruding cylindrical part  14   b  closely contacts the cap  61 , and the O-ring  71  is retained inside the enlarged diameter section  63  to prevent leakage of the silicone oil  21  from between the shaft part  32  and the cap  61 . Then, the thin protruding cylindrical part  14   b  and the cap  61  are sealed around tightly together with, for example, high-frequency welding. When the shaft part  32  protruding from the cap  61  is pressed into the attachment hole  82  of the driven gear  81 , the coupling band  83  is fitted into the coupling groove  35 , thereby completing the assembly of the rotary damper D.  
      An operation of the rotary damper D will be explained next. First, when the rotor  31  rotates in the clockwise direction in  FIG. 2 , the resistance part  36  rotates in the clockwise direction within the silicone oil  21 . Since viscosity and shear resistance of the silicone oil  21  acts on the resistance part  36 , the rotation of the rotor  31  is damped. Accordingly, rotation or movement of a gear, rack, or the like engaging the driven gear  81  attached to the rotor  31  is damped and slowed down.  
      When the rotor  31  rotates in the clockwise direction, on the downstream side of the resistance parts  36 , a part of the air mixed into the case  11  during the assembly moves and follows a negative pressure part generated at a downstream side of the sloping parts  39 B of the resistance parts  36 . Also, on the upstream side of the resistance parts  36 , a part of the air mixed into the case  11  during the assembly is gradually released between the inner perimeter surface  14   a  and the outer perimeter surfaces of the sloping parts  39 B, and moves to follow the negative pressure part generated at a downstream side of the sloping parts  39 B, after being gradually compressed between the inner perimeter surface  14   a  of the cylindrical wall part  14  and the outer perimeter surfaces of the sloping parts  39 A. The rest of the air mixed into the case  11  during the assembly passes above and below the radial flat plates  37  in a virtually non-compressed state, and moves so as to follow the negative pressure part generated at a downstream side of the sloping parts  39 B.  
      When the rotor  31  rotates in the counterclockwise direction in  FIG. 2 , the resistance parts  36  rotate in the counterclockwise direction within the silicone oil  21 . Since the viscosity and shear resistance of the silicone oil  21  acts on the resistance parts  36 , the rotation of the rotor  31  is damped. Accordingly, the rotation or movement of a gear, rack, or the like engaging the driven gear  81  attached to the rotor  31  is damped and slowed down.  
      When the rotor  31  rotates in the counterclockwise direction, a large part of the air following the negative pressure part generated at the downstream side of the sloping parts  39 B when the rotor  31  rotates in the clockwise direction passes above and below the radial flat plates  37  in a virtually non-compressed state, and moves following a negative pressure part generated at the downstream side of the sloping parts  39 A. A part of the air is gradually compressed between the inner perimeter surface  14   a  and the outer perimeter surfaces of the sloping parts  39 B, and then is gradually released between the inner perimeter surface  14   a  and the outer perimeter surfaces of the sloping parts  39 A. Incidentally, torque is generated at a part between the inner perimeter surface  14   a  of the cylindrical wall part  14  and the outer perimeter surface of the rotor  36 .  
      According to the first embodiment of the invention as described above, the sloping parts  39 A and  39 B (first sloping part and second sloping part) are provided with respect to the inner perimeter surface  14   a  of the cylindrical wall part  14 . Accordingly, a part of the air mixed into the case  11  during the assembly is gradually compressed between the inner perimeter surface  14   a  and the sloping parts  39 A (or sloping parts  39 B), and then is gradually released between the inner perimeter surface  14   a  and the sloping parts  39 B (or sloping parts  39 A). Therefore, even if the rotor  31  rotates in both directions, the air mixed into the case  11  is no longer released suddenly, so that it is possible to prevent the generation of a noise caused by the air mixed into the case  11 . Further, the sloping parts  39 A and  39 B are provided on the outer perimeter parts of the resistance parts  36  where a negative pressure tends to be generated most easily when the rotor  31  rotates, it is possible to effectively prevent the generation of a noise caused by the air mixed into the case  11 .  
       FIG. 3  is a perspective view of a rotor constituting a rotary damper according to a second embodiment of the invention, and  FIG. 4  is a sectional view of a radial pole taken along line  4 - 4  in  FIG. 3 . The same symbols are assigned to the same or corresponding parts shown in  FIG. 1  and  FIG. 2 , and their explanations are omitted. In these drawings, the rotor  31  made of a synthetic resin is held inside the case  11 , and is formed of the shaft part  32  partially protruding from the case  11 , and a plurality of resistance parts  36 , in the embodiment two provided at a 180-degree interval, extending horizontally and radially from the shaft part  32 .  
      Each of the resistance part  36  is formed of a radial pole  40  extending radially from the shaft part  32 , and an arc-shaped plate  42  provided on an outer perimeter edge of the radial pole  40  in the circumferential direction and facing the inner surface of the case  11 , that is, the inner perimeter surface  14   a  of the cylindrical wall part  14 .  
      As shown in  FIG. 4 , the above-mentioned radial poles  40  have a hexagonal cross-section. Two lower surfaces are sloping surfaces (sloping parts)  40   a  and  40   b  in which a center in a width direction moves toward and away from the inner surface  13   a  of the bottom part  13  of the case  11  from both ends in the width direction toward the center. Two upper surfaces are sloping surfaces (sloping parts)  40   c  and  40   d  in which a center in the width direction moves toward and away from the inner surface  61   a  of the cap  61  from both ends in the width direction toward the center.  
      When the rotor  31  rotates in the clockwise direction in  FIG. 3 , the sloping parts  40   a  become a first sloping part positioned on the upstream side of the resistance parts  36 , where the distance with respect to the inner surface  13   a  of the bottom part  13  gradually becomes narrower toward the downstream side. The sloping parts  40   b  become a second sloping part positioned on the downstream side of the resistance parts  36 , where the distance with respect to the inner surface  13   a  of the bottom part  13  gradually becomes wider toward the downstream side. The sloping parts  40   c  become a first sloping part positioned on the upstream side of the resistance parts  36 , where the distance with respect to the inner surface  61   a  of the cap  61  gradually becomes narrower toward the downstream side. The sloping parts  40   d  become a second sloping part positioned on the downstream side of the resistance parts  36 , where the distance with respect to the inner surface  61   a  of the cap  61  gradually becomes wider toward the downstream side. Accordingly, when the rotor  31  rotates in the counterclockwise direction in  FIG. 3 , the sloping parts  40   b  and  40   d  become the first sloping part, and the sloping parts  40   a  and  40   c  become the second sloping part.  
      Because the assembly and operation of the rotary damper D in the second embodiment are the same as in the first embodiment, their explanations are omitted.  
      When the rotor  31  rotates forward, the air mixed into the case  11  during the assembly moves so as to follow a negative pressure part generated at the downstream side of the arc-shaped plates  42  of the resistance parts  36 . When the rotor  31  rotates in reverse, the air following the negative pressure part generated at the downstream side of the arc-shaped plates  42  when the rotor  31  rotates [forward] does not pass between the inner perimeter surface  14   a  of the cylindrical wall part  14  and the outer perimeter surfaces of the arc-shaped plates  42  (resistance part  36 ), i.e. the torque generating part, and passes above and below the radial poles  40  and moves toward the negative pressure part generated at the downstream side of the arc-shaped plates  42  on the opposite side.  
      Thus, the air passing above and below the radial poles  40 , for example, is gradually compressed between the inner perimeter surfaces  14   a  and  61   a  and the sloping surfaces  40   a  and  40   c  (or sloping surfaces  40   b  and  40   d ), and then is gradually released between the inner perimeter surfaces  14   a  and  61   a  and the sloping surfaces  40   b  and  40   d  (or sloping surfaces  40   a  and  40   c ). In the second embodiment, the same effect as in the first embodiment can be obtained. Also, because the sloping surfaces  40   a  to  40   d  are provided along the radial direction, the generation of noise can be prevented without depending on a position of the air mixed into the case  11 , thereby increasing torque and a range of adjusting the torque.  
       FIG. 5  is a sectional view of a rotor constituting a rotary damper according to a third embodiment of the invention. The same symbols are assigned to the same or corresponding parts as in FIGS.  1  to  4 , and their explanations are omitted.  FIG. 5  is a sectional view similar to  FIG. 4 . A only difference from the rotor shown in  FIG. 3  is an elliptical sectional shape of the radial poles constituting the rotor. The rotor  31  made of a synthetic resin shown in  FIG. 5  is held inside the case  11 , and is formed of the shaft part  32  partially protruding from the case  11 , and two resistance parts  36  provided at a 180-degree interval and extending horizontally and radially from the shaft part  32 .  
      Each of the resistance part  36  is formed of the radial pole  41  extending radially from the shaft part  32 , and the arc-shaped plate  42  provided on the outer perimeter edge of this radial pole  41  in the circumferential direction and facing the inner surface of the case  11 , that is, the inner perimeter surface  14   a  of the cylindrical wall part  14 .  
      The above-mentioned radial poles  41  have an elliptical sectional shape with a horizontal long axis (parallel to the inner surface  13   a  of the bottom part  13  and the inner surface  61   a  of the cap  61 ) and a vertical short axis (perpendicular to the inner surface  13   a  of the bottom part  13  and the inner surface  61   a  of the cap  61 ). The surface on the lower side is formed in the sloping surfaces (sloping parts)  41   a  and  41   b  in which the center in the width direction moves toward and away from the inner surface  13   a  of the bottom part  13  of the case  11  from both ends in the width direction toward the center. The surface on the upper side is formed in the sloping surfaces (sloping parts)  41   c  and  41   d  in which the center in the width direction moves toward and away from the inner surface  61   a  of the cap  61  from both ends in the width direction toward the center.  
      When the rotor  31  rotates in the clockwise direction in  FIG. 3 , the sloping surface  41   a  becomes a first sloping part positioned on the upstream side of the resistance part  36 , where the distance gradually becomes narrower toward the downstream side with respect to the inner surface  13   a  of the bottom part  13 , and the sloping surface  41   b  becomes a second sloping part positioned on the downstream side of the resistance part  36 , where the distance gradually becomes wider toward the downstream side with respect to the inner surface  13   a  of the bottom part  13 . Also, the sloping surface  41   c  becomes a first sloping part positioned on the upstream side of the resistance part  36 , where the distance gradually becomes narrower toward the downstream side with respect to the inner surface  61   a  of the cap  61 , and the sloping surface  41   d  becomes a second sloping part positioned on the downstream side of the resistance part  36 , where the distance gradually becomes wider toward the downstream side with respect to the inner surface  61   a  of the cap  61 .  
      Also, when the rotor  31  rotates in the counterclockwise direction in  FIG. 3 , the sloping surfaces  41   b  and  41   d  become the first sloping part, and the sloping surfaces  41   a  and  41   c  become the second sloping part. Because the assembly and operation of the rotary damper D in the third embodiment are the same as in the first embodiment, their explanations are omitted. Also, because the flow (movement) of the air mixed into the case  11  during the assembly is the same as in the second embodiment, its explanation is omitted. In the third embodiment, the same effect as in the first or second embodiment can be obtained.  
       FIG. 6  is a perspective view of a rotor constituting a rotary damper according to a fourth embodiment of the invention, and  FIG. 7  is a sectional view taken along line  7 - 7  in  FIG. 6 . The same symbols are assigned to the same or corresponding parts as in FIGS.  1  to  5 , and their explanations are omitted. In these drawings, the rotor  31  made of a synthetic resin is held inside the case  11 , and is formed of the shaft part  32  partially protruding from the case  11 , and the resistance part  36  comprising a circular flat plate  43  with a circular planar shape connected horizontally to the shaft part  32 .  
      Also, on the circular flat plate  43  (resistance part  36 ), as shown in  FIG. 7 , there are provided three rectangular holes (slits)  44  extending radially at positions separated by 120 degrees. In addition, there are provided sloping parts  45 A and  45 B extending from both sides in the circumferential direction toward each of the holes  44  and having inclined upper and lower sides moving toward and away from each other.  
      When the rotor  31  rotates in the clockwise direction in  FIG. 6 , the sloping parts  45 A become the first sloping part positioned on the upstream side of the resistance part  36 , where the distance gradually becomes narrower toward the downstream side with respect to the inner surface  13   a  of the bottom part  13  and the inner surface  61   a  of the cap  61 . The sloping parts  45 B become the second sloping part positioned on the downstream side of the resistance part  36 , where the distance gradually becomes wider toward the downstream side with respect to the inner surface  13   a  of the bottom part  13  and the inner surface  61   a  of the cap  61 . Also, when the rotor  31  rotates in the counterclockwise direction in  FIG. 6 , the sloping parts  45 B become the first sloping part, and the sloping parts  45 A become the second sloping part.  
      In the fourth embodiment, torque generation parts are located between the inner perimeter surface  14   a  and the outer perimeter surface of the rotor  36  (circular flat plate  43 ), and between the upper and lower surfaces of the rotor  36  (circular flat plate  43 ) and the inner surfaces  13   a  and  61   a . Because the assembly and operation of the rotary damper D in the fourth embodiment are the same as in the first embodiment, their explanations are omitted.  
      As for the flow (movement) of the air mixed into the case  11  during the assembly, for example, the air is gradually compressed between the sloping parts  45 A (or sloping parts  45 B) and the inner surfaces  13   a  and  61   a , and then is gradually released between the sloping parts  45 B (or sloping parts  45 A) and the inner surfaces  13   a  and  61   a . Also, the air flowing into one of the holes  44  from the sloping parts  45 A or the sloping parts  45 B moves following a negative pressure part generated at the downstream side of the sloping parts  45 A or the sloping parts  45 B, and tends not to flow into the other of the holes  44 .  
      In the fourth embodiment, the same effect as in the first-third embodiments can be obtained. Also, in the fourth embodiment, even if the holes  44  are not provided, an effect same as that in the first to third embodiments can be obtained.  
       FIG. 8  is a perspective view of a rotor constituting a rotary damper according to a fifth embodiment of the invention. The same symbols are assigned to the same or corresponding parts in FIGS.  1  to  7 , and their explanations are omitted.  
      The rotor  31  made of a synthetic resin shown in  FIG. 8  is held inside the case  11 , and is formed of the shaft part  32  partially protruding from the case  11 , and the resistance part  36  comprising a radial flat plate  46  having an I-cut circle planar shape extending from the shaft part  32  horizontally and radially at a 180-degree interval.  
      On the radial flat plate  46  (resistance part  36 ), there are provided sloping surfaces (sloping parts)  46   a  and  46   b  extending to an outer perimeter on both upper sides at the upstream side and the downstream side in the rotational direction.  
      When the rotor  31  rotates in the clockwise direction, the sloping surfaces  46   a  become the first sloping part positioned on the upstream side of the resistance part  36 , where the distance gradually becomes narrower toward the downstream side with respect to the inner surface  61   a  of the cap  61 , and the sloping surfaces  46   b  become the second sloping part positioned on the downstream side of the resistance part  36 , where the distance gradually becomes wider toward the downstream side with respect to the inner surface  61   a  of the cap  61 . Also, when the rotor  31  rotates in the counterclockwise direction, the sloping surfaces  46   b  become the first sloping part, and the sloping surfaces  46   a  become the second sloping part.  
      Because the assembly and operation of the rotary damper D in the fifth embodiment are the same as in the first embodiment, their explanations are omitted. Also, because the flow (movement) of the air mixed into the case  11  during the assembly is the same as in the second embodiment, its explanation is omitted. In the fifth embodiment also, the same effect as in the first to fourth embodiments can be obtained.  
       FIG. 9  is a perspective view of a rotor constituting a rotary damper according to a sixth embodiment of the invention. The same symbols are assigned to the same or corresponding parts as in FIGS.  1  to  8 , and their explanations are omitted.  
      The rotor  31  made of a synthetic resin shown in  FIG. 9  is held inside the case  11 , and is formed of the shaft part  32  protruding from the case  11 , and two resistance parts  36  extending horizontally and radially at a 180-degree interval from the shaft part  32 . Also, each of the resistance parts  36  is formed of a radial flat plate  47  connected to the shaft part  32 , and a flat diamond-shaped projection  48  connected to an outer perimeter surface of the radial flat plate  47  and having sloping surfaces  48   a  and  48   b  at an upper side and a lower side, respectively.  
      When the rotor  31  rotates in the clockwise direction, the sloping surfaces  48   a  become the first sloping part positioned on the upstream side of the resistance parts  36 , where the distance gradually becomes narrower going downstream with respect to the inner surface  13   a  of the bottom part  13  and the inner surface  61   a  of the cap  61 . The sloping surfaces  48   b  become the second sloping part positioned on the downstream side of the resistance parts  36 , where the distance gradually becomes wider going downstream with respect to the inner surface  13   a  of the bottom part  13  and the inner surface  61   a  of the cap  61 . Also, when the rotor  31  rotates in the counterclockwise direction, the sloping surfaces  48   b  become the first sloping part, and the sloping surfaces  48   a  become the second sloping part.  
      Because the assembly and operation of the rotary damper D in the sixth embodiment are the same as in the first embodiment, their explanations are omitted. Also, because the flow (movement) of the air mixed into the case  11  during the assembly is the same as in the second embodiment, its explanation is omitted. In the sixth embodiment also, the same effect as in the first to fifth embodiments can be obtained.  
       FIG. 10  is a plan view of a rotor constituting a rotary damper according to a seventh embodiment of the invention. The same symbols are assigned to the same or corresponding parts as in FIGS.  1  to  9 , and their explanations are omitted.  
      The rotor  31  made of a synthetic resin shown in  FIG. 10  is held inside the case  11 , and is formed of the shaft part  32  partially protruding from the case  11 , and the resistance parts  36  extending outward horizontally and radially at a 90-degree interval from the shaft part  32  and comprising spherical union bodies  49  having spheres connected like dumplings. Also, on each of the spherical union bodies  49  (resistance parts  36 ), there are provided hemispheric surfaces (sloping parts)  49   a  and  49   b  on both upper sides at the upstream side and the downstream side in the rotational direction.  
      When the rotor  31  rotates in the clockwise direction, the hemispheric surfaces  49   a  become the first sloping part positioned on the upstream side of the resistance part  36 , where the distance gradually becomes narrower toward the downstream side with respect to the inner surface  13   a  of the bottom part  13 , the inner perimeter surface  14   a  of the cylindrical wall part  14 , and the inner surface  61   a  of the cap  61 , and the hemispheric surfaces  49   b  become the second sloping part positioned on the downstream side of the resistance part  36 , where the distance gradually becomes wider toward the downstream side with respect to the inner surface  13   a  of the bottom part  13 , the inner perimeter surface  14   a  of the cylindrical wall part  14 , and the inner surface  61   a  of the cap  61 . Also, when the rotor  31  rotates in the counterclockwise direction, the hemispheric surfaces  49   b  become the first sloping part, and the hemispheric surfaces  49   a  become the second sloping part.  
      Because the assembly and operation of the rotary damper D in this seventh embodiment are the same as in the first embodiment, their explanations are omitted. Also, because the flow (movement) of the air mixed into the case  11  during assembly is the same as in the second embodiment, its explanation is omitted. In the seventh embodiment also, the same effect as in the first to sixth embodiments can be obtained.  
       FIG. 11  is a perspective view of a rotor constituting a rotary damper according to an eighth embodiment of the invention. The same symbols are assigned to the same or corresponding parts in FIGS.  1  to  10 , and their explanations are omitted.  
      The rotor  31  made of a synthetic resin shown in  FIG. 11  is held inside the case  11 , and is formed of the shaft part  32  partially protruding from the case  11 , and the resistance part  36  comprising a radial flat plate  50  having a I-cut circle planar shape and extending horizontally and radially at a 180-degree interval from the shaft part  32 . Also, on the radial flat plate  50  (resistance part  36 ), there are provided plural triangularly shaped cut-outs  51 A and  51 B recessed from an outside of the radial flat plate  50  toward an inside of the radial flat plate  50 , that is, having a long side of the radial flat plate  50  as a base, on both sides at the upstream side and the downstream side in the rotational direction.  
      When the rotor  31  rotates in the clockwise direction, the cut-outs  51 A become the first sloping part positioned on the upstream side of the resistance part  36 , where the distance gradually becomes narrower toward the downstream side with respect to the inner surface  13   a  of the bottom part  13  and the inner surface  61   a  of the cap  61 , and the cut-outs  51 B become the second sloping part positioned on the downstream side of the resistance part  36 , where the distance gradually becomes wider toward the downstream side with respect to the inner surface  13   a  of the bottom part  13  and the inner surface  61   a  of the cap  61 . Also, when the rotor  31  rotates in the counterclockwise direction, the cut-outs  51 B become the first sloping part, and the cut-outs  51 A become the second sloping part.  
      Because the assembly and operation of the rotary damper D in the eighth embodiment are the same as in the first embodiment, their explanations are omitted. Also, because the flow (movement) of the air mixed into the case  11  during assembly is the same as in the second embodiment, its explanation is omitted. In the eighth embodiment, the same effect as in the first to sixth embodiments can be obtained.  
      In the above-mentioned embodiments, the examples have been shown, in which the rotor  31  is rotatable supported with the bearing part  16  on the case  11  and the recess  33  on the shaft part  32 . The rotor may be constituted such that the recess is provided on the case and the bearing part is provided on the shaft. Also, in the embodiments, the torque is generated mainly between the inner perimeter surface  14   a  of the case  11  and the outer perimeter surface of the resistance body  36 . It also may be constituted such that the torque is generated mainly between the inner perimeter surface of the cap and the outer perimeter surface of the resistance body.  
      Also, in the embodiments, the housing is formed of the case  11  and the cap  61 . The receiving part  15  for the silicone oil  21  is provided in the case  11 . The through-hole  62  is provided in the cap  61  for inserting the shaft part  32  of the rotor  31 , and the O-ring  71  is provided for sealing between the cap  61  and the shaft part  32  to prevent leakage of the silicone oil  21 . It also may be constituted such that the receiving part for the silicone oil is provided in the cap, and the through-hole for inserting the shaft part of the rotor is provided in the case. The O-ring is provided for sealing between the case and the shaft to prevent leakage of the silicone oil.  
      Also, the silicone oil  21  is used as the viscous fluid, but other viscous fluids functioning in the same manner, for example such as grease, also can be used. Also, the resistance part  36  is integrally formed on the shaft part  32 , but it also may be constituted such that the shaft part and the resistance part are molded separately, and have a square shaft and a square hole to rotate integrally.  
      The disclosure of Japanese Patent Application No. 2003-349465, filed on Oct. 8, 2003, is incorporated in the application.  
      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.