Patent Publication Number: US-6341969-B1

Title: Rotary connector

Description:
FIELD OF THE INVENTION 
     The present invention relates to a rotary connector used for the steering device of an automobile. More specifically, it relates to a rotary connector which establishes electric connections between an electric circuit secured to the steering column and an electric circuit attached on the steering wheel to be rotated, using a flexible flat cable. 
     BACKGROUND OF THE INVENTION 
     Conventionally, such a rotary connector described above, is made of following components: 
     (a) an outer case fixed to the steering column of an automobile; 
     (b) an inner case attached to the steering wheel shaft rotating with the steering wheel; and 
     (c) a flat cable for establishing electric connections between the outer case side and the inner case side. 
     Such rotary connectors are broadly categorized into two types in terms of the winding way of the flat cable: 
     1. the winding that is spiral in one direction between the outer case and the inner case; 
     2. the winding that is reversed in direction at a midpoint of the flat cable. 
     Comparing two rotary connectors having a same outside dimension in which the flat cable is wound according to the two ways, the “reversed” winding can save the length of the flat cable, with reduced parts cost. The rotary connector with the “reversed” winding has therefore been popular in recent years. 
     Now will be explained about conventional rotary connectors with the flat cable spirally wound in one direction, referring to FIGS. 9 to  12 . 
     FIG. 9 is a cross-sectional view and FIG. 10 is an exploded perspective view of a conventional rotary connector. The conventional rotary connector, as shown in FIGS. 9 and 10, comprises following components: 
     (a) cylindrical outer case  1  with the top and bottom surfaces open; 
     (b) inner case  2  accommodated in outer case  1  rotatably relative to outer case  1 ; 
     (c) cover  3  which is fixed to outer case  1  to cover the opening at the bottom of outer case  1 ; and 
     (d) flexible flat cable  5  which is housed in ring-shaped space  4  between outer case  1  and inner case  2 . 
     Inner case  2  is made of lid  2 A which covers the top opening of outer case  1 , and inner cylinder  2 B having shaft hole  2 C which protrudes downwardly from the center of the rear surface of lid  2 A. 
     Ring-shaped space  4  is formed between inner wall  1 A of outer case  1  and inner cylinder  2 B of inner case  2 . Wound in several turns, flat cable  5  is accommodated in space  4 . Flexible flat cable  5  has band-shaped appearance, covering a plurality of conductive wires together. The inside end of flat cable  5  is connected to terminal  5 A that is secured to inner case  2 . Terminal  5 A is further connected to inner connector  6 . On the other hand, the outside end of flat cable  5  is connected to outer connector  7 , which is fixed to outer case  1  and coupled to an external electric circuit. 
     In addition, elastic tongue-shaped piece  8 , such as an insulating sheet, is attached to the inside end of flat cable  5 . The end of tongue-shaped piece  8  is inserted in terminal  5 A and is secured. A conventional rotary connector has such constitution described above. Outer case  1  of the rotary connector is fixed to a steering column (not shown) of an automobile. The steering wheel shaft (not shown) is inserted into shaft hole  2 C of inner cylinder  2 B of inner case  2 . Formed in such structure described above, a conventional rotary connector is attached to the steering device of an automobile. 
     Outer connector  7 , which is secured to outer case  1 , is coupled to an electric circuit fixed to the steering column on the car body side. On the other hand, inner connector  6 , which is secured to inner case  2 , is coupled to an electric circuit within the steering wheel. In this manner, the electric connection between the steering wheel and the steering column is established via flat cable  5 . 
     Now will be described how the rotation of steering wheel effects the winding state of flat cable  5  in the conventional rotary connector structured above. 
     FIG. 9 shows the state of flat cable  5  being wound evenly on the side of inner wall  1 A of outer case  1  and the side of inner cylinder  2 B of inner case  2 . In this state, the steering wheel is held at a neutral position. Rotating the steering wheel from the neutral position rotates inner case  2  attached to the steering wheel shaft. 
     When the steering wheel is rotated in a clockwise direction, flat cable  5 , shown in the cross-sectional view of FIG. 11, is wound on the side of inner cylinder  2 B of inner case  2 . In this case, flat cable  5  is wound more on the side of inner cylinder  2 B than the side of inner wall  1 A of outer case  1 . 
     On the other hand, when the steering wheel is rotated, from the state shown in FIG. 9, in a counterclockwise direction, flat cable  5  is now wound more on the side of inner wall  1 A, as shown in the cross-sectional view of FIG.  12 . At this time, the inside end of flat cable  5  is guided by tongue-shaped piece  8 . This protects flat cable  5  from buckling or deformation indicated by the broken line in FIG.  12 . 
     As described above, the conventional rotary connector employs tongue-shaped piece  8  to prevent the inside end of flat cable  5  from buckling or deformation when the steering wheel is rotated in a counterclockwise direction. This, however, inconveniently not only increases the number of parts of the rotary connector but also consumes the time for assembling. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problems discussed above and aims to provide an economical and easy to assemble rotary connector with minimized number of parts. 
     To achieve the object described above, the rotary connector of the present invention comprises: 
     (a) a cylindrical outer case with the top and bottom surfaces open; 
     (b) an inner case accommodated in the outer case rotatably relative to the outer case, having a lid covering the top opening of the outer case and also having an inner cylinder protruding downwardly from the center of the rear surface of the lid; 
     (c) a cover fixed to the outer case covering the bottom opening of the outer case; 
     (d) a flexible flat cable housed in a ring-shaped space, with its inner and outside ends secured to inner and outer cases, respectively; 
     (e) a recess formed closely to where the inside end is fixed on the inner cylinder of the inner case; 
     (f) a guide piece formed at the recess so as to fit along the periphery of the inner cylinder, having its one end formed in one piece with the bottom surface of the lid of the inner case,; and 
     (g) a gap formed between the inner wall of the guide piece and the periphery of the recess on the inner cylinder. 
     On the tip of the guide piece described above, an edge portion is formed so as to tilt in the direction of the periphery of the inner cylinder. 
     Besides, a portion adjacent to the inside end of the flat cable is passed through the gap, which is formed between the inner wall of the guide piece and the periphery of the recess on the inner cylinder. The flat cable is then guided out from the tilted edge portion of the guide piece. This guiding makes the flat cable abut against an R-shaped edge surface of the tilted edge portion of the guide piece when the flat cable is rewound. With slightly warped, the flat cable is unreeled from the side of the inner cylinder. The structure described above therefore not only protects the flat cable from buckling or deformation, but also minimizes the number of parts. It is thus possible to obtain an easy to assemble rotary connector with a low cost. 
     As a preferred embodiment, the rotary connector according to the present invention may employ a flat cable having an U-shaped reversed portion so that the winding of the flat cable on the side of the inner wall of the outer case is opposite in direction, via the reversed portion, to the winding on the side of the inner cylinder of the inner case. To be precise, a guide-ring having a guide-gap through which a reversed portion of the flat cable passes is accommodated, as well as the flat cable, in the ring-shaped space formed between the outer and inner cases such that the guide piece is rotatably relative to the outer case. The guide-ring reverses the winding direction of the flat cable in the space between the outer and inner cases, saving the length of the flat cable. It is thus possible to provide a cost-saved rotary connector. 
     Rotary Connector 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross-sectional view of a rotary connector in accordance with a first preferred embodiment of the present invention. 
     FIG. 2 shows an exploded perspective view of the rotary connector illustrated in FIG.  1 . 
     FIG. 3 shows a perspective view of the essential part of the rotary connector illustrated in FIG.  1 . 
     FIG. 4 shows a cross-sectional view of the rotary connector illustrated in FIG. 1, with its joint portion shaped linearly or in a circular arc. 
     FIG. 5 shows a cross-sectional view of the rotary connector illustrated in FIG. 1, with a flexible member attached to the clearance. 
     FIG. 6 shows a cross-sectional view of the rotary connector illustrated in FIG. 1, with a projected holder formed. 
     FIG. 7 shows a cross-sectional view of a rotary connector in accordance with a second preferred embodiment of the present invention. 
     FIG. 8 shows an exploded perspective view of the rotary connector illustrated in FIG.  7 . 
     FIG. 9 shows a cross-sectional view of a conventional rotary connector. 
     FIG. 10 shows an exploded perspective view of the conventional rotary connector. 
     FIG. 11 shows a cross-sectional view of the conventional rotary connector in which the flat cable is wound tightly. 
     FIG. 12 shows a cross-sectional vies of the conventional rotary connector in which the flat cable is rewound. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings, FIG.  1  through FIG.  8 . Same parts as explained in the prior art are identified with same reference numerals, and their detailed description is omitted. 
     First Preferred Embodiment 
     FIG. 1 shows a cross-sectional view of a rotary connector in accordance with a first preferred embodiment of the present invention. FIG. 2 shows an exploded perspective view of the rotary connector illustrated in FIG.  1 . 
     The rotary connector, shown in FIGS. 1 and 2, in accordance with the first preferred embodiment comprises: 
     (a) cylindrical outer case  1  with the top and bottom surfaces open; 
     (b) inner case  12  accommodated in the outer case  1  rotatably relative to outer case  1 ; 
     (c) cover  3  fixed to outer case  1  to cover the bottom opening of the outer case  1 ; 
     (d) flexible flat cable  5  housed in ring-shaped space  4 , with its inside and outside ends secured to inner and outer cases, respectively; 
     (e) recess  12 C formed closely to where the inside end of flat cable  5  is fixed on inner cylinder  12 B of inner case  12 ; 
     (f) guide piece  13  formed at recess  12 C, having its one end formed in one piece with the bottom surface of lid  12 A of the inner case  12 ; and 
     (g) gap  14  formed between the inner wall of guide piece  13  and the periphery of recess  12 C on the inner cylinder. 
     The structure described below is the same as that in a conventional rotary connector: 
     (a) cylindrical outer case  1  with the top and bottom surfaces open; 
     (b) cover  3  fixed to outer case  1 , covering the bottom opening of outer case  1 ; 
     (c) inner case  12  provided with lid  12 A covering the top opening of outer case  1 , and with inner cylinder  12 B having shaft hole  12 D protruding downwardly from the center of the rear surface of the lid  12 A; 
     (d) flexible flat cable  5  which is wound in several turns and accommodated in ring-shaped space  4  that is formed between inner wall  1 A of outer case  1  and inner cylinder  12 B of inner case  12 . Flat cable  5  has band-shaped appearance, covering a plurality of conductive wires together. 
     (e) terminal  5 B fixed to inner case  12  is disposed at the inside end of flat cable  5 ; 
     (f) terminal  5 B is coupled to inner connector  6 ; 
     (g) inner connector  6  is coupled to an electric circuit within the steering wheel; 
     (h) outer connector  7  fixed to outer case  1  is coupled to the outside end of flat cable  5 ; and 
     (i) outer connector  7  is coupled to an external electric circuit. 
     In regard to the structure described above (a) through (i), there is no difference between the present invention and the prior art. The novelty in the rotary connector of the preferred embodiment is, however, in formation of recess  12 C and guide piece  13 . Recess  12 C is formed on the outer wall of inner cylinder  12 B of inner case  12 , to be precise, recess  12 C is formed closely to where the inside end of flat cable  5  is fixed on the inner cylinder  12 B. 
     In addition, guide piece  13  is disposed at recess  12 C. One end of guide piece  13  is formed in one piece with the bottom surface of lid  12 A of inner case  12 . It may be formed in one piece with the periphery of inner cylinder  2 B. The periphery of guide piece  13 , which is shaped in a circular arc, is formed almost along the periphery of inner cylinder  12 B. Edge portion  13 A of circumferentially directed tip of guide piece  13  tilts in the periphery direction (FIG.  3 ). Besides, gap  14  is formed between the periphery of recess  12 C and the inner wall of guide piece  13 . A portion adjacent to the inside end of flat cable  5  is passed through gap  14 . Flat cable  5  is then guided out from circumferentially tilted edge portion  13 A of the tip of guide piece  13 . 
     In the rotary connector of the first preferred embodiment structured above, outer case  1  is secured to the steering column (not shown) of an automobile. The steering wheel shaft (not shown) is inserted into shaft hole  12 D of inner cylinder  12 B of inner case  12 . In this manner, the rotary connector of the first preferred embodiment is attached to the steering device in a car body. Outer connector  7 , which is fixed to outer case  1 , is coupled to an electric circuit in the steering column on the side of a car body, while inner connector  6 , which is fixed to inner case  12 , is coupled to an electric circuit within the steering wheel. An electric connection between the steering wheel and the steering column is thus established via flat cable  5 . In regard to such workings, there is no difference between the present invention and the prior art. 
     Now will be described how the rotation of the steering wheel effects the winding state of flat cable  5  in the rotary connector structured above in accordance with the first preferred embodiment. 
     FIG. 1 shows the state of flat cable  5  being wound evenly on the side of inner wall  1 A of outer case  1  and the side of inner cylinder  12 B of inner case  12 . In this state, the steering wheel is held at a neutral position. 
     Rotating the steering wheel from the neutral position rotates inner case  12  attached to the steering wheel shaft. 
     When the steering wheel is rotated in a clockwise direction, flat cable  5  is wound on the side of inner cylinder  12 B of inner case  12 . In this case, the winding of flat cable  5  is in a tightened state, being wound more on the side of inner cylinder  12 B than the side of inner wall  1 A. 
     On the other hand, when the steering wheel is rotated, from the state shown in FIG. 1, in a counterclockwise direction, flat cable  5  is now wound more on the side of inner wall  1 A, that is, the winding of flat cable  5  is in a rewound state. The workings responsive to the rotation of the steering wheel are the same as those of the conventional rotary connector. 
     When flat cable  5  is rewound, however, it is guided out from the gap between circumferentially tilted edge portion  13 A, which is formed on the tip of guide piece  13 , and the periphery of recess  12 C. This guiding makes the flat cable abut against the R-shaped edge surface of the edge portion of guide piece  13 A when flat cable t is unreeled. With slightly warped, the flat cable is unreeled from the side of the inner cylinder  12 B. Such structure relieves the stress applied to flat cable  5  at which the portion abuts against the R-shaped edge surface of edge portion  13 A. With the stress relieved gradually, flat cable  5  is unreeled from the side of inner cylinder  12 B to the side of inner wall  1 A of outer case  1 . 
     When the steering wheel is rotated in a counterclockwise direction, as described above, flat cable  5  abuts against the R-shaped edge surface of tilted edge portion  13 A of guide piece  13 . Then with slightly warped, flat cable  5  is unreeled from the side of inner cylinder  12 B. According to the embodiment, it becomes possible not only to protect the flat cable from buckling or deformation, but also to realize an easy to assemble and economical rotary connector with a minimized number of parts. 
     As shown in the cross-sectional view of FIG. 4, joint  12 E connecting the periphery of recess  12 C of inner case  12  and the periphery of inner cylinder  12 B is structured to be linear or rather circular arc with a gentle slope. With such structure, flat cable  5  is unreeled from the side of inner cylinder  12 B, guided along the linear or circular arc shaped surface of joint  12 E. This smoothly shaped joint  12 E, shown in FIG. 4, applies a force evenly to the surface of flat cable  5  for smooth winding. 
     As illustrated in the cross-sectional view in FIG. 5, elastic member  15 , such as a rubber or other elastomer materials, is disposed in gap  14  between the periphery of recess  12 C of inner case  12  and the inner wall of guide piece  13 . With the help of elastic member  15 , an area adjacent to the inside end of flat cable  5  resiliently abuts against guide piece  13 . The abutment minimizes a rattle of flat cable  5  in gap  14 , providing a smooth winding of flat cable  5  with no abnormal rattling sound. 
     Besides, as shown in the cross-sectional view in FIG. 6, between terminal  5 B and guide piece  13 , projected holder  16  is disposed on the periphery of recess  12 C on inner case  12 . On the both sides of holder  16 , exposed recess  17  is formed. With the structure, a proximity area to the inside end of flat cable  5  is held from terminal  5 B along holder  16  and exposed recess  17 . This arrangement increases the friction between the proximity area to the inside end of flat cable  5  and the periphery of recess  12 C or the inner wall of guide piece  13 . Therefore, a force, which is generated when rotating the steering wheel, applied to the inside end of flat cable  5  can be reduced. 
     Second Preferred Embodiment 
     FIG. 7 shows a cross-sectional view of a rotary connector in accordance with a second preferred embodiment of the present invention. FIG. 8 shows an exploded perspective view of the rotary connector illustrated in FIG.  7 . 
     The rotary connector of the second preferred embodiment, shown in FIGS. 7 and 8, is made of following components: 
     (a) cylindrical outer case  21  with the top and bottom surfaces open; 
     (b) inner case  12  accommodated in outer case  21  rotatably relative to outer case  21 , 
     (c) cover  23  fixed to outer case  21  to cover the bottom opening of the outer case  21 ; 
     (d) flexible flat cable  50  with reversed portion  50 C formed, which is housed in ring-shaped space  4  that is defined by outer case  21  and inner case  12 ; and 
     (e) guide-ring  24 , which has guide-gap  24 A through which reversed portion  50 C of flat cable  50  is inserted, is accommodated in ring-shaped space  4 . 
     In regard to the structure described below, the rotary connector of the embodiment is no different from that of the first embodiment, that is: 
     (a) cylindrical outer case  21  with the top and bottom surface open; 
     (b) cover  23  is fixed to outer case  21 , covering the bottom opening of outer case  21 ; 
     (c) inner case  12  is provided with lid  12 A covering the top opening of outer case  1 , and with inner cylinder  12 B having shaft hole  12 D protruding downwardly from the center of the rear surface of the lid  12 A; 
     (d) ring-shaped space  4  is formed between inner wall  21 A of outer case  21  and inner cylinder  12 B of inner case  12 ; 
     (e) guide piece  13  is formed at recess  12 C disposed on inner cylinder  12 B of inner case  12 , having its one end formed in one piece with the bottom surface of lid  12 A of inner case  12 ; 
     (f) A proximity area to the inside end of flat cable  50  is inserted into gap  14  that is formed between the periphery of recess  12 C of inner cylinder  12 B and the inner wall of guide piece  13 ; 
     (g) edge portion  13 A of circumferentially directed tip of guide piece  13 , tilting in the periphery of guide piece  13  direction, from which flat cable  50  is guided out; 
     (h) terminal  50 B fixed to inner case  12  is disposed at the inside end of flat cable  50 ; 
     (i) terminal  50 B is coupled to inner connector  60 ; 
     (j) inner connector  60  is coupled to an electric circuit within the steering wheel; 
     (k) outer connector  70  fixed to outer case  21  is coupled to the outside end of flat cable  50 ; and 
     (l) outer connector  70  is coupled to an external electric circuit. 
     The structural difference from the first preferred embodiment is, according to the rotary connector of the second embodiment, in employing guide-ring  24  and flat cable  50  having U-shaped reversed portion  50 C. To be precise, flat cable  50  having U-shaped reversed portion  50 C is housed in ring-shaped space  4 . With reversed portion  50 C, the winding on the side of the proximity to inner wall  21 A of outer case  21  is opposite in direction to the winding on the side of the proximity to inner cylinder  12 B of inner case  12 . 
     Guide-ring  24  having guide-gap  24 A through which reversed portion  50 C of flat cable  50  is inserted is rotatably accommodated, as well as flat cable  50 , in ring-shaped space  4 . 
     In the rotary connector of the second preferred embodiment structured above, outer case  21  is secured to the steering column (not shown) of an automobile. The steering wheel shaft (not shown) is inserted into shaft hole  12 D of inner cylinder  12 B of inner case  12 . In this manner, the rotary connector of the second preferred embodiment is attached to the steering device in a car body. Outer connector  70 , which is fixed to outer case  21 , is coupled to an electric circuit in the steering column on the side of a car body, while inner connector  60 , which is fixed to inner case  12 , is coupled to an electric circuit within the steering wheel. An electric connection between the steering wheel and the steering column is thus established via flat cable  50 . In regard to such workings, there is no difference between the first and the second embodiments. 
     Now will be described how the rotation of steering wheel effects the winding state of flat cable  50  in the rotary connector structured above in accordance with the second preferred embodiment. 
     FIG. 7 shows the state of flat cable  50  being wound evenly on the side of inner wall  21 A of outer case  21  and the side of inner cylinder  12 B of inner case  12 . In this state, the steering wheel is held at a neutral position. 
     Rotating the steering wheel from the neutral position rotates inner case  12  attached to the steering wheel shaft. The rotation of the steering wheel changes the winding state of flat cable  50 . As the steering wheel rotates, guide-ring  24  also rotates, responsive to reeled or unreeled flat cable  50 , in the same direction with inner case  12 . As inner case  12  rotates, flat cable  50  is guided by guide-gap  24 A of guide-ring  24  through which reversed portion  50 C is inserted. As a result, flat cable  50  is wound, responsive to the rotation of the steering wheel, on the side of inner cylinder  12 B of inner case  12  or the side of inner wall  21 A of outer case  21 . That is, when inner case  12  rotates in a clockwise direction, flat cable  50  is wound on the side of inner cylinder  12 B of inner case  12 . As flat cable  50  rotates, reversed portion  50 C pushes side-wall  24 B of guide-gap  24 A of guide-ring  24 . This brings a clockwise rotation to guide-ring  24 , so that the winding of flat cable  50  is in a tightened state. On the other hand, when inner case  12  rotates in a counterclockwise direction, flat cable  50  is unreeled from the side of inner cylinder  12 B of inner case  12 . Pushed side-wall  24 C of guide-gap  24 A by reversed portion  50 C, guide-ring  24  now rotates in a counterclockwise direction, resulting that flat cable  50  is in a rewound state. The rotary connector of the second embodiment works in such way. 
     As described above, in ring-shaped space  4  formed between outer case  21  and inner case  12 , flat cable  50 , which is guided by guide-gap  24 A of guide-ring  24  through which reversed portion  50 C is inserted, changes its winding in opposite direction at reversed portion  50 C. This structure advantageously saves the length of flat cable  50 , comparing to that of a conventional rotary connector. 
     The present invention described above not only protects the flat cable from buckling or deformation, but also minimizes the number of parts. It is thus highly effective in providing an easy to assemble rotary connector with a low cost.