Patent Publication Number: US-2013237369-A1

Title: Rotation transmission mechanism and rotary connector

Description:
CLAIM OF PRIORITY 
     This application claims benefit of Japanese Patent Application No. 2012-052920 filed on Mar. 9, 2012, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to a rotation transmission mechanism that can transmit rotation by the engagement of a plurality of gears and a rotary connector including the rotation transmission mechanism, and more particularly, to a rotation transmission mechanism of which at least one of a plurality of gears can be deformed in a radial direction and a rotary connector including the rotation transmission mechanism. 
     2. Description of the Related Art 
     A rotary connector is used in an automobile or the like to transmit an electrical signal or an optical signal or to supply electric power between a stationary body and a rotating body. Specifically, when a steering wheel is provided with an air bag or switches used to operate an audio system or the like, electrical communication and the like need to be made between the steering wheel as a rotating body and a vehicle as a stationary body. Accordingly, a rotary connector is installed between the steering wheel and the vehicle. 
     In a rotary connector, a stationary housing provided on a stationary body and a movable housing provided on a rotating body are disposed coaxially, an annular space is formed between an outer cylindrical body formed on the stationary housing and an inner cylindrical body formed on the movable housing, and a flat cable is wound and received in the annular space. Both end portions of the flat cable are connected to the stationary housing and the movable housing. Accordingly, when the movable housing is rotated with the rotation of the rotating body, the flat cable is wound or loosened. Therefore, an electrical connection with the stationary body is maintained regardless of the rotation of the rotating body. 
     In such a rotary connector, it is possible to reduce the length of the flat cable that is required for obtaining the same rotatable range of the rotary connector by inverting the middle portion of the flat cable. As such a rotary connector, there is a rotary connector disclosed in, for example, Japanese Unexamined Utility Model Registration Application Publication No. 6-50283. 
     The rotary connector where the length of the flat cable is reduced by the inversion of the flat cable employs a structure where the stationary housing is provided with an internal gear (outer gear), the movable housing is provided with a sun gear, the internal gear and the sun gear face each other, a planetary gear engaged with both the internal gear and the sun gear is provided, and the planetary gear is provided with an inversion maintaining portion maintaining the inversion of the flat cable. 
     However, in this case, for smooth operation, a certain level of backlash is needed between the planetary gear and the internal gear and the sun gear in consideration of the deformation of the gears, and the like. For this reason, when an automobile vibrates, the gears collide with each other, which causes rattling to be generated. This is not limited to the rotary connector, and is a general problem in a rotation transmission mechanism that transmits rotation by the engagement of a plurality of gears. 
     SUMMARY 
     A rotation transmission mechanism includes a plurality of gears to be engaged with each other and transmits power by the rotation of the gears. At least one of the plurality of gears includes a tooth-side base portion and an opposite base portion that are disposed coaxially and connected to each other by connecting portions. The tooth-side base portion is formed in the shape of a ring and includes a tooth row on one peripheral surface thereof. The opposite base portion faces a peripheral surface of the tooth-side base portion opposite to the peripheral surface of the tooth-side base portion on which the tooth row is formed. Protruding portions are formed on the peripheral surface of the tooth-side base portion facing the opposite base portion. The connecting portions extend from the protruding portions toward the peripheral surface of the opposite base portion facing the tooth-side base portion. A portion, which is connected to the tooth-side base portion, of each connecting portion and a peripheral surface-tangential direction of the tooth-side base portion form an acute angle. 
     According to the rotation transmission, the connecting portions extend from the protruding portions so that an acute angle is formed between the peripheral surface-tangential-direction of the tooth-side base portion and the connecting portion. Accordingly, the connecting portions are apt to be deformed in the radial direction, and are not apt to be deformed in the circumferential direction. Therefore, the gears provided with the connecting portions can be deformed only in the radial direction, the plurality of gears can be smoothly operated even though backlash is eliminated, and torsion is not generated on the gears in the circumferential direction, so that the life span of the rotation transmission mechanism is lengthened. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a rotary connector according to an embodiment; 
         FIG. 2  is a plan view showing the disposition of each gear; 
         FIG. 3  is a perspective view of a planetary gear; 
         FIG. 4  is a partial enlarged view of a sun gear; 
         FIG. 5  is a schematic plan view showing the engagement between the planetary gear and the sun gear; 
         FIG. 6  is a cross-sectional view at a position, where the planetary gear is present, in the longitudinal cross-sectional view of the rotary connector; 
         FIG. 7  is a partial enlarged view of the sun gear that is provided with connecting portions including wide portions; and 
         FIG. 8  is a schematic plan view showing the engagement between the planetary gear and the sun gear. 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Embodiments of the invention will be described in detail with reference to the drawings.  FIG. 1  is an exploded perspective view of a rotary connector according to this embodiment. Further,  FIG. 6  is a cross-sectional view at a position, in the longitudinal cross-sectional view of the rotary connector, where a planetary gear is present. The rotary connector according to this embodiment includes a stationary housing  1  that is fixed to a steering column part of an automobile and a movable housing  2  that is rotated together with a steering wheel. Flat cables  3 , which form an electrical connection between the stationary housing  1  and the movable housing  2 , are wound and received in an annular space  5  ( FIG. 6 ) that is formed between the stationary housing  1  and the movable housing  2 . 
     An upper case  20  including an outer cylindrical body  21  and a lower case  25  including a bottom plate  26  are connected and integrated with each other by snap-fitting or the like, so that the stationary housing  1  is formed. A substantially ring-shaped ring portion  22 , which protrudes inward from the upper end of the outer cylindrical body  21 , is formed at the upper case  20 . The ring portion  22  is integrally provided with an upper connection portion  23  that protrudes outward from the outer periphery of the outer cylindrical body  21 . 
     The lower case  25  includes a wall portion  25   a  that is erected from the outer edge portion of the bottom plate  26 , and an internal gear  12  is formed on the inner peripheral wall of the wall portion  25   a.  A planetary gear  11  is engaged with the internal gear  12 , and the planetary gear  11  is engaged with a sun gear  10  that is provided on the movable housing  2 . The structure of each gear will be described in detail below. The lower case  25  includes an opening  27  into which a steering shaft is inserted. The planetary gear  11  rotates and revolves on the inner surface of the bottom plate  26 . 
     Further, a lower connection portion  28 , which is integrated with the upper connection portion  23  when the lower case  25  is integrated with the upper case  20 , is formed on the outer periphery of the lower case  25 . The lower connection portion  28  is provided with a connector (not shown) electrically connecting the flat cables  3 , which are led to the stationary side, to the vehicle side. 
     The movable housing  2  includes an upper rotor  30  and a lower rotor  35 . The upper rotor  30  includes a ring-shaped top plate portion  31  that is positioned above the annular space  5 , and an inner cylindrical body  32  that protrudes from the inner edge portion of the top plate portion  31  toward the bottom plate  26  of the lower case  25 . The inner cylindrical body  32  is disposed coaxially with the outer cylindrical body  21 , and faces the inner peripheral surface of the outer cylindrical body  21  with the annular space  5  interposed therebetween. Meanwhile, the lower rotor  35  includes a ring-shaped ring portion  36  and a cylindrical portion  37  that is erected from the inner edge portion of the ring portion  36 . 
     The top plate portion  31  of the movable housing  2  includes movable-side connection portions  33  that receive lead blocks (not shown) connected to the inner end portions of the flat cables  3 . External connectors (not shown) connected to, for example, an air bag system, a horn switch circuit, and the like provided on a steering portion are connected to the lead blocks. Further, the cylindrical portion  37  of the lower rotor  35 , which is inserted from the opening  27  of the lower case  25 , is connected to the inner cylindrical body  32  of the upper rotor  30 , which is inserted into the stationary housing  1 , by snap-fitting. When the upper and lower rotors  30  and  35  are connected to each other as described above, the ring portion  36  of the lower rotor  35  comes into contact with the outer surface of the bottom plate  26  of the lower case  25  and the movable housing  2  is rotatably supported by the stationary housing  1 . 
     Conductor wires of each of the flat cables  3  are coated with a flexible resin film. In this embodiment, a first flat cable  3   a  and a second flat cable  3   b  are received and wound in the annular space  5 . The winding direction of the first flat cable  3   a  is reversed at a first inverted portion  3   c,  and the winding direction of the second flat cable  3   b  is reversed at a second inverted portion  3   d.    
     The inner end portion of each of the flat cables  3  is fixed to the movable housing  2  through the lead block (intermediate connection body) (not shown), and the outer end portion of each of the flat cables is fixed to the stationary housing  1  through a lead block. Further, when the movable housing  2  is rotated relative to the stationary housing  1 , each of the flat cables  3  is wound on the outer peripheral surface of the inner cylindrical body  32  and is unwound from the outer peripheral surface. 
     A rotating ring body (inversion maintaining portion)  4  is disposed on the inner surface of the bottom plate  26  in the annular space  5  as shown in  FIG. 6 . The planetary gear  11  is rotatably supported by the rotating ring body  4 . Accordingly, when the movable housing  2  is rotated, the rotating ring body  4  is rotated with the rotation and revolution of the planetary gear  11 . 
     Meanwhile, as shown in  FIG. 1 , the rotating ring body  4  includes a ring-shaped main body portion  40 . Further, the rotating ring body  4  includes a first opening (inversion maintaining portion)  41  into which the first inverted portion  3   c  of the first flat cable  3   a  is inserted and a second opening (inversion maintaining portion)  42  into which the second inverted portion  3   d  of the second flat cable  3   b  is inserted, at different positions on the main body portion  40  in a circumferential direction. For this reason, the inverted shapes of the first and second inverted portions  3   c  and  3   d  of the respective flat cables  3  are maintained by the first and second openings  41  and  42 , regardless of the rotational position of the movable housing  2 . Here, the main body portion  40  includes peripheral wall portions  40   a  that face the inner wall of the outer cylindrical body  21  and the outer wall of the inner cylindrical body  32 . Meanwhile, for example, columnar bodies, cylindrical bodies, rotatable rollers, or the like, which are formed so as to protrude from the planetary gear  1 , other than the first and second openings of the rotating ring body  4  may be applied as the inversion maintaining portions, and are disposed within the inverted portions (first and second inverted portions  3   c  and  3   d ) of the flat cable  3 . 
     With this structure, it is possible to stably maintain the shapes of the first and second inverted portions  3   c  and  3   d  of the flat cable  3  regardless of the rotation direction or the rotational speed of the movable housing  2 . Accordingly, it is possible to improve the quality and reliability of the rotary connector by making a disturbance in the deformation of the flat cable  3  be difficult to generate. Further, since the plurality of openings are formed, a plurality of inverted flat cables  3  can be easily wound by a small number of members. As a result, it is possible to reduce costs. 
     As shown in  FIG. 6 , the sun gear  10  is mounted on a first opposite surface  32   a,  which faces the bottom plate  26  of the lower case  25 , of the inner cylindrical body  32  of the movable housing  2 . Meanwhile, the first opposite surface  32   a  will be described in detail below. When the movable housing  2  is supported so as to be rotatable relative to the stationary housing  1 , the sun gear  10  faces the internal gear  12  of the stationary housing  1  in the radial direction. 
     As shown in  FIG. 6 , the flat cables  3  are wound in the annular space  5  on the inner periphery and the outer periphery of the rotating ring body  4 , respectively. The first and second opposite surfaces  32   a  and  32   b  (contact surface portions), which face the bottom plate  26  (lower case  25 ), are formed on the radially outer portion of the lower portion of the inner cylindrical body  32  with a level difference therebetween. The first opposite surface  32   a  is formed on the radially inner portion of the inner cylindrical body  32 , and the second opposite surface  32   b  is formed on the radially outer portion of the inner cylindrical body  32 . The sun gear  10  is mounted on the first opposite surface  32   a  as described above. 
     The rotating ring body  4  includes flange portions  43  that are formed at the lower end portion thereof so as to protrude outward and inward. Further, an inner edge portion  43   a  of the flange portion  43 , which protrudes inward, is positioned inside the outer peripheral wall of the inner cylindrical body  32  in the radial direction. Meanwhile, an outer edge portion  43   b  of the flange portion  43 , which protrudes outward, extends into an outer gap portion  21   a,  which is formed by a step portion formed at the lower portion of the outer cylindrical body  21 , and is positioned outside the inner peripheral wall of the outer cylindrical body  21  in the radial direction. Accordingly, the flange portions  43  support the lower end portions of the respective flat cables  3 . Further, a space in which each of the flat cables can be moved in the vertical and radial direction is narrowly defined by the lower surfaces of the ring portion  22  and the top plate portion  31 , the upper surface of the flange portion  43 , and the above-mentioned peripheral wall portions  40   a.  Accordingly, even though a vehicle vibrates up and down while running, it is possible to reduce sound that is generated by the collision between the respective flat cables and the inner surfaces of the ring portion  22  and the bottom plate  26 . Furthermore, since the inner edge portion  43   a  of the flange portion  43  always comes into elastic contact with the first opposite surface  32   a  due to elastic bias forces of elastic arm portions  11   c,  the planetary gear  11  and the rotating ring body  4  do not rattle in a vertical direction even though a vehicle vibrates while running. Accordingly, it is possible to prevent rattling from being generated. 
       FIG. 2  is a plan view showing the disposition of each gear. The planetary gear  11  is engaged with the sun gear  10  and the internal gear  12  that are disposed coaxially. Accordingly, the planetary gear  11  revolves in the circumferential direction while rotating with the rotation of the movable housing  2 . The rotating ring body  4  is rotated on the inner surface of the bottom plate  26  by the rotation and the revolution of the planetary gear  11 . 
     The planetary gear  11  will be described in detail.  FIG. 3  is a perspective view of the planetary gear  11 . The planetary gear  11  includes a tooth row  11   a  that is formed of a plurality of teeth arranged in the circumferential direction of the outer peripheral surface. Further, a protruding portion  11   b  is formed at the central portion of the planetary gear  11  so as to protrude in the axial direction. The protruding portion  11   b  is rotatably fitted to a fitting recess  44  of the rotating ring body  4  ( FIG. 6 ). Accordingly, when the planetary gear  11  rotates and revolves, the rotating ring body  4  is rotated in the annular space  5 . 
     Moreover, slits  11   e  are formed in the planetary gear  11  in the circumferential direction so as to include a plurality of elastic arm portions  11   c.  Protrusions  11   d  are formed on the end portions of the elastic arm portions  11   c  (elastic contact portions) so as to protrude toward the rotating ring body  4 . Since the elastic arm portion  11   c  is formed in the shape of a cantilever so as to be thinner than other portions of the planetary gear  11 , the elastic arm portion  11   c  can be elastically deformed. Since the planetary gear  11  is disposed in  FIG. 6  so that the elastic arm portions  11   c  (not shown) are deformed so as to be bent, the protrusions  11   d  receive a resistive force (reaction force) from the rotating ring body  4 . Accordingly, the planetary gear  11  generates an elastic bias force that is directed downward in the axial direction. 
     The planetary gear  11  pushes up the rotating ring body  4  and presses the rotating ring body  4  against the first opposite surface  32   a  (inner cylindrical body  32 ) by the elastic bias forces that are generated by the elastic arm portions  11   c.  Accordingly, since the rotating ring body  4  does not rattle in the annular space  5  even though a vehicle vibrates while running, it is possible to prevent rattling from being generated. 
     The sun gear  10  will be described in detail.  FIG. 4  is a partial enlarged view of the sun gear  10 . The sun gear  10  includes a tooth-side base portion  10   a  and an opposite base portion  10   b  that are integrated by a plurality of connecting portions  10   c  formed in the circumferential direction. The tooth-side base portion  10   a  forms the outer periphery, is formed in the shape of a ring, and includes a tooth row  10   d  on one peripheral surface thereof. The opposite base portion  10   b  forms the inside, that is, the center-side of the tooth-side base portion  10   a,  and faces the peripheral surface of the tooth-side base portion  10   a  opposite to the peripheral surface of the tooth-side base portion  10   a  on which the tooth row  10   d  is formed. 
     Protruding portions  10   e,  which protrude toward the opposite base portion  10   b,  are formed on the peripheral surface of the tooth-side base portion  10   a  facing the opposite base portion  10   b.  Further, the connecting portions  10   c  extend toward the opposite base portion  10   b  from the positions, which are separated from the tooth-side base portion  10   a,  on the protruding portions  10   e.  A portion of the connecting portion  10   c  between a tooth-side root portion  10   f,  which is a root portion connected to the tooth-side base portion  10   a,  and an opposite-side root portion  10   g,  which is a portion connected to the opposite base portion  10   b,  is formed in the shape of a gentle curve. Meanwhile, since the connecting portion  10   c  is formed so as to be thinner and narrower than other portions of the sun gear  10 , the connecting portion  10   c  can be elastically deformed. 
       FIG. 4  shows a peripheral surface-tangential direction of the tooth-side base portion  10   a  at the position where the protruding portion  10   e  is formed, and a direction in which a portion of the connecting portion  10   c  near the tooth-side root portion  10   f  extends. An angle θ 1  between these directions is a small acute angle, and the tooth-side root portion  10   f  and the tooth-side base portion  10   a  are substantially parallel to each other. In detail, the tooth-side root portion  10   f  extends from the protruding portion  10   e  so as to be parallel to the peripheral surface-tangential direction while being separated from the peripheral surface of the tooth-side base portion  10   a.  Further, the connecting portion  10   c  extends from the tooth-side root portion  10   f  toward the peripheral surface of the opposite base portion  10   b  facing the tooth-side base portion  10   a  so that θ 1  is gradually increased. Furthermore, since the connecting portion  10   c  extends the protruding portion  10   e  that protrudes from the tooth-side base portion  10   a,  a space, which is elastically deformed so as to be close to the tooth-side base portion  10   a,  is also secured. For this reason, a portion, which is connected to the tooth-side base portion  10   a,  of the connecting portion  10   c  is apt to be elastically deformed in the radial direction of the sun gear  10 . Meanwhile, elastic deformation is not apt to occur in the circumferential direction of the sun gear  10 . 
     The connecting portion  10   c  is curved so that an angle formed by the connecting portion  10   c  gradually becomes larger than an angle formed by the peripheral surface-tangential direction of the tooth-side base portion  10   a  from the tooth-side root portion  10   f  toward the opposite-side root portion  10   g.  Accordingly, an angle θ 2  between a direction in which the opposite-side root portion  10   g  extends and the peripheral surface-tangential direction of the opposite base portion  10   b  is larger than the angle θ 1 . Further, since the connecting portion  10   c  is formed so as to become wide toward the opposite-side root portion  10   g,  the strength of a portion of the connecting portion  10   c  close to the opposite-side root portion  10   g  is high. For this reason, a portion, which is connected to the opposite base portion  10   b,  of the connecting portion  10   c  is not apt to be elastically deformed both in the radial direction and the circumferential direction of the sun gear  10 . 
       FIG. 5  is a schematic plan view showing the engagement between the planetary gear  11  and the sun gear  10 .  FIG. 5  emphatically shows that a gap between the sun gear  10  and the internal gear  12  is narrowed due to a temperature change, more than in reality. When a gap between the sun gear  10  and the internal gear  12  is narrowed, the planetary gear  11  is barely deformed but presses the sun gear  10 , which can be easily deformed, in the radial direction. Accordingly, the sun gear  10  is deformed in the radial direction. That is, the portion, which is close to the tooth-side root portion  10   f,  of the connecting portion  10   c  of the sun gear  10  is elastically deformed. Meanwhile, the strength of the portion of the connecting portion  10   c  close to the opposite-side root portion  10   g  is high and is not easily elastically deformed, and the portion of the connecting portion  10   c  close to the tooth-side root portion  10   f  is also not easily elastically deformed in the circumferential direction. Accordingly, since the sun gear  10  is deformed only in the radial direction, it is possible to prevent the shortening of the life span of the sun gear  10  that is caused by the torsional deformation generated when deformation is generated in the circumferential direction. 
     If the protruding portion  10   e  is formed on the tooth-side base portion  10   a  of the sun gear  10  and an angle (an angle θ 1  of  FIG. 4 ) between the connecting portion  10   c  extending from the protruding portion  10   e  and the peripheral surface-tangential direction of the tooth-side base portion  10   a  at the protruding portion  10   e  is set to be an acute angle as described above, the connecting portion  10   c  is formed so as to be capable of being elastically deformed only in the radial direction. Accordingly, even though backlash between the planetary gear  11  and the sun gear  10  and the internal gear  12  is set to zero, the respective gears can be smoothly engaged and rotated. Therefore, since the respective gears are smoothly engaged without rattling in plan view even though a vehicle vibrates while running, it is possible to prevent rattling from being generated. Further, even though foreign substances enter the gaps between the planetary gear  11  and the sun gear  10  and the internal gear  12 , the occurrence of a disturbance in the engagement and rotation of the respective gears can be avoided by the elastic deformation of the planetary gear  11  and the sun gear  10 . 
     Furthermore, since the rotating ring body  4  provided on the planetary gear  11  is biased upward in the axial direction by the elastic arm portions  11   c,  the inner edge portion  43   a  of the flange portion  43  always comes into elastic contact with the second opposite surface  32   b.  Accordingly, since the planetary gear  11  and the rotating ring body  4  do not rattle in the vertical direction even though a vehicle vibrates up and down while running, it is possible to prevent rattling from being generated. 
     The connecting portion  10   c  may be provided with a wide portion  10   h.    FIG. 7  is a partial enlarged view of the sun gear  10  that is provided with the connecting portions  10   c  including the wide portions  10   h.  The wide portion  10   h  is a portion that is formed between the opposite-side root portion  10   g  and the tooth-side root portion  10   f  of the connecting portion  10   c  so as to be wider than other portions. The wide portion  10   h  is a portion that is to be pushed by an ejector pin when the sun gear  10  is manufactured by molding a resin, and also has a function of restricting the deformation of the connecting portion  10   c.    
       FIG. 8  is a schematic plan view showing the engagement between the planetary gear  11  and the sun gear  10 . Since the wide portion  10   h  comes into contact with the tooth-side base portion  10   a  when the sun gear  10  is pressed against the planetary gear  11  and deformed in the radial direction, the further deformation of the connecting portion  10   c  is restricted. Accordingly, it is possible to prevent the shortening of the life span of the sun gear that is caused by the excessive deformation of the connecting portion  10   c.    
     In the rotary connector according to this embodiment, the sun gear  10  has been adapted so as to be capable of being elastically deformed in the radial direction by the connecting portions  10   c.  However, one or more of the sun gear  10 , the planetary gear  11 , and the internal gear  12  may be adapted so as to be capable of being elastically deformed in the radial direction by the same structure. 
     Further, in this embodiment, the protruding portions  10   e  have been formed on the tooth-side base portion  10   a  of the sun gear  10  and the portion of the connecting portion  10   c  close to the protruding portion  10   e  has been adapted so as to be easily deformed in the radial direction. However, the protruding portions may be formed on the opposite base portion  10   b  of the sun gear  10 . That is, even though the protruding portions are formed on the opposite base portion and the direction of curvature of the connecting portion is opposite to the above-mentioned direction, it is possible to obtain the same function. 
     The embodiment of the invention has been described above, but the invention is not limited to this embodiment and may be applied in various ways within the scope of the invention. A rotation transmission mechanism, which includes the sun gear  10 , the planetary gear  11 , and the internal gear  12  and is used in the rotary connector, has been described in this embodiment. However, as long as a rotation transmission mechanism includes a plurality of gears to be engaged with each other and can transmit power by the rotation of the gears, the invention can be applied to the rotation transmission mechanism. Accordingly, it is possible to obtain an effect of smoothly engaging the respective gears and rotating the gears even though backlash between the gears is set to zero. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims of the equivalents thereof.