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BACKGROUND OF THE INVENTION 
     The present invention relates to a vehicle door opening/closing device that drives a vehicle door used to open and close a door opening formed in a vehicle body. 
     Patent document 1 describes an example of a vehicle door opening/closing device known in the prior art. As shown in  FIG. 9 , the vehicle door opening/closing device includes a guide rail  91 , which is fixed to a side portion of a vehicle body, and a guide roller member  93 , which is fixed to a vehicle door  92  and movably engaged with the guide rail  91 . An electric motor  97  serving as a drive source is set on the vehicle body. The electric motor  97  rotates and drives a drum  96 . A cable  95  is selectively wound around and unwound from the drum  96 . The cable includes two ends  95   a  and  95   b , each coupled to the guide roller member  93 . 
     The cable  95 , which extends from the drum  96  in the front-rear direction of the vehicle, runs around and between two pulleys  94   a  and  94   b , which are located at the front side and the rear side of the guide rail  91 . The two ends  95   a  and  95   b  are coupled to the guide roller member  93 . 
     In such a conventional structure, when the drum  96  and the cable  95  transmits the drive force of the electric motor  97  to the guide roller member  93 , the guide roller member  93  moves in the front-rear direction of the vehicle along the guide rail  91 . The vehicle door  92  moves integrally with the guide roller member  93  and opens and closes the door opening. 
     Such a known vehicle door opening/closing device that is arranged on a quarter panel of a vehicle body is also known including a guide rail, an electric motor, a drum, a cable, and two pulleys (refer to patent document 2). 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2008-128322 
     Patent Document 2: Japanese Laid-Open Patent Publication No. 2010-105494 
     SUMMARY OF THE INVENTION 
     In the vehicle door opening/closing device described in patent document 1, when moving the vehicle door  92  to a fully-closed position, the front end  95   b  of the cable  95  approaches the front pulley  94   b  together with the guide roller member  93 . In particular, the end  95   b  of the cable  95  is further moved by a significant amount toward the front pulley  94   b  when the guide roller member  93  moves beyond its stroke toward the front due to the inertial force of the vehicle door  92 . Accordingly, to avoid interference between the front pulley  94   b  and the front end  95   b  of the cable  95 , the front pulley  94   b  needs to be separated toward the front from where the end  95   b  of the cable  95  is located at the fully-closed position of the vehicle door  92 . 
     The front end of a guide rail usually lies along the movement path of a guide roller member in the vicinity of the fully-closed position of the vehicle door. The vehicle door is pushed toward the outer side in the vehicle widthwise direction immediately after the vehicle door starts to open from the fully-closed position or pulled toward the inner side in the vehicle widthwise direction immediately before the fully-closed position. Thus, the front end of the guide rail is curved and inclined toward the inner side in the vehicle widthwise direction (refer to patent document 2). Accordingly, at the fully-closed position of the vehicle door, the front pulley  94   b , which is separated toward the front from the front end  95   b  of the cable  95 , is arranged at the inner side in the vehicle widthwise direction in correspondence with the curve of the guide rail. In this case, in particular, the vehicle door opening/closing device in which the guide rail is arranged on the quarter panel of the vehicle body increases the amount of the area accommodating the front pulley that is bulged into the passenger compartment. This reduces the space in the passenger compartment and adversely affects the aesthetic appearance of the interior. 
     It is an object of the present invention to provide a vehicle door opening/closing device capable of obtaining a sufficient clearance between an end of a cable and a front pulley without increasing the amount bulged into the passenger compartment of the area accommodating components such as a front pulley and the like at the front side of the guide rail. 
     To solve the above problem, the present invention includes a guide rail configured to be arranged on a quarter panel at a rear side of a door opening formed in a side portion of a vehicle body. The guide rail is configured to extend in a front-rear direction and includes an inclined portion on a front end, and the inclined portion is inclined toward a vehicle interior. A guide roller member is configured to be coupled to a vehicle door that opens and closes the door opening. The guide roller member includes a roller that can roll on the guide rail. A drive member is configured to be fixed to the vehicle body. The drive member includes a drive source and a drum that is rotated and driven by the drive source. A front pulley and a rear pulley are located at a front side and a rear side of the guide rail. A cable is wound around the drum and runs along the front pulley and the rear pulley to change directions. The cable includes two ends that are each coupled to the guide roller member. A closing operation cable portion, which is a portion of the cable extending from the front pulley to the guide roller member, is located at an outer side of the guide rail, and a corresponding one of the ends is coupled to the guide roller member at the rear of the roller. An opening operation cable portion, which is a portion of the cable extending from the rear pulley to the guide roller member, is located in the guide rail, and a corresponding one of the ends is coupled to the guide roller member. 
     In the present invention, the closing operation cable portion of the cable is arranged at the outer side of the guide rail and includes an end that is coupled to the guide roller member at the rear of the roller. Accordingly, the end of the closing operation cable portion and the coupling portion in the guide roller member at the fully closed position are separated from the front pulley, which is arranged at the front of the end. Thus, a sufficient clearance between the end of the closing operation cable portion and the front pulley may be obtained without increasing the amount bulged into the passenger compartment of the area accommodating components such as a front pulley and the like at the front side of an inclined portion of the guide rail. Thus, the space in the passenger compartment is not reduced, and the aesthetic appearance of the interior is not adversely affected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a main portion of a vehicle door opening/closing device according to one embodiment of the present invention. 
         FIG. 2  is a cross-sectional view taken along the section line  2 - 2  in  FIG. 1  and showing the main portion of the device of  FIG. 1 . 
         FIG. 3  is a perspective view showing a front side of a center rail and the peripheral structure of the center rail. 
         FIG. 4  is a perspective view showing a rear side of the center rail and a peripheral structure of the center rail. 
         FIG. 5A  is a perspective view showing the device of  FIG. 1  in a coupled condition. 
         FIG. 5B  is a cross-sectional view taken along the section line  5 B- 5 B in  FIG. 1  and showing the device of  FIG. 1  in the coupled condition. 
         FIG. 6  is a schematic view showing a vehicle such as an automobile to which the device of  FIG. 1  is applied. 
         FIG. 7  is a plan view showing a sliding door arranged at a fully-closed position or a fully-open position. 
         FIG. 8  is a partially enlarged view showing a guide roller unit. 
         FIG. 9  is a schematic view showing a conventional structure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of the present invention will now be described with reference to  FIGS. 1 to 8 . Hereinafter, the front-rear direction of the vehicle is referred to as “front-rear direction”, and the upper side and the lower side in the vertical direction of the vehicle are respectively referred to as “upper side” and “lower side”. The inner side in the vehicle widthwise direction toward the interior of the passenger compartment is referred to as the “vehicle interior side”, and the outer side in the vehicle widthwise direction toward the exterior of the passenger compartment is referred to as the “vehicle exterior side”. 
     As shown in  FIG. 6 , an upper rail  11  and a lower rail  12  extending in the front-rear direction are respectively set along an upper edge and a lower edge of a door opening  10   a  formed in a side portion of a vehicle body of the vehicle body  10 . A center rail  13 , which serves as a guide rail extending in the front-rear direction, is set on a quarter panel  10   b  at the rear of the door opening  10   a . A sliding door  20 , which serves as a vehicle door, is movably supported in the front-rear direction by the upper rail  11 , the lower rail  12 , and the center rail  13  with guide roller units  14  and  15  and a guide roller unit  16 , which serves as a guide roller member. When moved in the front-rear direction to open and close the door opening  10   a , the sliding door  20  moves the guide roller units  14  to  16  on the upper rail  11 , the lower rail  12 , and the center rail  13 , respectively. 
     The center rail  13  and the guide roller unit  16  will now be further described. As shown in  FIG. 7 , the center rail  13  is formed from, for example, a metal plate and includes a curved portion  13   a  at a longitudinally middle portion. The center rail  13  extends in the front-rear direction, that is, the opening and closing direction of the sliding door  20 . The center rail  13  includes the curved portion  13   a , an inclined portion  13   b  located at the front end, and a straight portion  13   c . The inclined portion  13   b  is inclined toward the vehicle interior from the front end of the curved portion  13   a , and the straight portion  13   c  extends toward the rear from the rear end of the curved portion  13   a . A trimming, that is, a lining  50  that forms an ornamental surface of the vehicle body  10  in the passenger compartment includes a bulging portion  50   a  that bulges toward the vehicle interior in conformance with the front end of the inclined portion  13   b  of the center rail  13 . The vehicle body  10  rotationally supports a front pulley  17 , which is located proximate to the front end of the inclined portion  13   b  of the center rail  13 , and rotationally supports a rear pulley  18 , which opposes the rear end of the straight portion  13   c  of the center rail  13 . The front pulley  17  and the rear pulley  18  each have an axis extending in the vertical direction of the vehicle. 
     A drive member  30  is fixed to the vehicle body  10  and located proximate to the center rail  13 . The drive member  30  includes a drive motor  31 , which serves as a drive source, and a drum  32 , which is rotated and driven by the drive motor  31 . A front cable  33  and a rear cable  34  are each wound around the drum  32  and each include an inner end fixed to the drum  32 . 
     The front cable  33  extends toward the front through the interior of an outer tube  35 , which is arranged between the drum  32  and the front pulley  17 , and is then exposed from the outer tube  35  to the exterior. Further, the front cable  33  is directed toward the rear after running along the front pulley  17  and changing directions. The rear cable  34  extends toward the rear through the interior of an outer tube  36 , which is arranged between the drum  32  and the rear pulley  18 , and is then exposed from the outer tube  36  to the exterior. Further, the rear cable  34  is directed toward the front after running along the rear pulley  18  and changing directions. 
     As shown in  FIGS. 1 and 2 , the center rail  13  has a substantially C-shaped cross-sectional shape that is open toward the vehicle exterior and the sliding door  20 . The center rail  13  includes a lower wall portion that forms a first roller guide  13   d  and an upper wall portion of which distal section is downwardly bent to form a second roller guide  13   e.    
     The guide roller unit  16  includes, for example, a base plate  21  formed by a metal plate, a load roller  22  and front and rear vertical rollers  23 . 
     The base plate  21  is rotationally coupled to a bracket  51 , which is fixed to the sliding door  20 . The base plate  21  includes a coupling wall portion  21   a , which is coupled to the bracket  51  pivotally about an axis O 1  extending in the vertical direction of the vehicle, and an extended wall portion  21   b , which extends from the upper end of the coupling wall portion  21   a  toward the center rail  13 . 
     The base plate  21  includes a raised wall portion  21   c , which rises from the front portion at the upper end of the extended wall portion  21   b , and front and rear support pieces  21   d , which are bent toward the vehicle interior side from the upper end of the raised wall portion  21   c . The load roller  22  is supported by the upper end of the raised wall portion  21   c . Further, the load roller  22  is axially supported by a support pin  24  extending along an axis intersecting the center rail  13 . As shown in  FIG. 2 , the vertical rollers  23  are axially supported by the support pieces  21   d . Specifically, each vertical roller  23  is supported by a support pin  25  that extends along an axis O 2  in the vertical direction of the vehicle. The support pins  25  extend through the support pieces  21   d  in the vertical direction of the vehicle, and the upper portions of the support pins  25  support the vertical rollers  23 . The lower ends of the support pins  25  that extend through the support pieces  21   d  form substantially circular rods  26  including substantially circular flanges  26   a  at the lower ends. In other words, the rods  26  are formed integrally with the support pins  25  and are coaxial with the vertical rollers  23 . 
     The base plate  21  includes a support piece  21   e  extending from the rear side of the upper end of the extended wall portion  21   b  to the vehicle interior side below the center rail  13 . A support pin  27  extending along an axis O 3  in the vertical direction of the vehicle is attached to the support piece  21   e . The upper end of the support pin  27  extends through the support piece  21   e  and forms a substantially circular rod-shaped front cable coupling portion  28  including a substantially oval-shaped flange  28   a  at the upper end. The longitudinal direction of the flange  28   a  substantially coincides with the longitudinal direction of the center rail  13 , that is, the front-rear direction. As shown in the enlarged view of  FIG. 8 , the front cable coupling portion  28  is located proximate to the rear rod  26  (hereinafter also referred to as “rear cable coupling portion  26 A”) as viewed from above. More specifically, the front cable coupling portion  28  partially overlaps the rear cable coupling portion  26 A as viewed from above. 
     Referring to  FIG. 1 , the portion of the front cable  33  directed toward the rear after running along the front pulley  17  and changing directions toward the rear (hereinafter also referred to as “closing operation cable portion  33 A”) is located at the lower side and the outer side of the center rail  13 , and the end  37  of the front cable  33  is coupled to the front cable coupling portion  28 . More specifically, as shown in  FIG. 5A , the end  37  has a substantially oblong tubular shape and an opening in the vertical direction of the vehicle to receive the flange  28   a . When the front cable coupling portion  28  is received in the end  37 , the end  37  is engaged with the flange  28   a  so that the end  37  cannot be separated from the flange  28   a . In the closing operation cable portion  33 A, tension is produced in the extending direction (front-rear direction) in the usage state after coupling the end  37 . This restricts separation of the end  37  from the front cable coupling portion  28 . The end  37  engaged with the front cable coupling portion  28  is located toward the rear of the load roller  22 . 
     The portion of the rear cable  34  directed toward the front after running along the rear pulley  18  and changing directions (hereinafter referred to as “opening operation cable portion  34 A”) is located in the center rail  13 , and the end  38  of the rear cable  34  is hooked to the rear cable coupling portion  26 A. More specifically, as shown in  FIG. 5B , the end  38  includes a substantially semicircular holder  38   a , and a substantially Q-shaped separation stopper  38   b , which is formed from a resin material and fitted into the holder  38   a . The holder  38   a  and the separation stopper  38   b  both face the rear cable coupling portion  26 A and are open toward the vehicle interior. When the end  38  is pushed against the rear cable coupling portion  26 A in the open direction of the holder  38   a , the separation stopper  38   b  is elastically deformed and widened. As a result, the rear cable coupling portion  26 A is fitted to the separation stopper  38   b , and the end  38  is hooked to the rear cable coupling portion  26 A with the flange  26   a  restricting separation of the end  38 . In the opening operation cable portion  34 A, tension is produced in the extending direction (front-rear direction, that is, direction substantially orthogonal to the opening direction of the holder  38   a ) in the usage state after coupling the end  38 . This restricts separation of the end  38  from the rear cable coupling portion  26 A. 
     The front pulley  17 , the rear pulley  18 , and the peripheral structure of the front pulley  17  and the rear pulley  18  will now be described. 
     As shown in  FIG. 3 , a front case  41 , which is formed from, for example, a resin, is fastened to the quarter panel  10   b  in conformance with the front end of the center rail  13 , and a grommet  42 , which is formed from, for example, a resin, is fitted to the front case  41  immediately below the center rail  13 . The front case  41  rotationally accommodates the front pulley  17 , and the grommet  42  guides the front cable  33  (closing operation cable portion  33 A), which is directed toward the rear after changing directions at the front pulley  17  in the front case  41 , to the lower side of the center rail  13 , that is, the exterior of the vehicle. 
     An arcuate cable guide  43 , which is formed from, for example, a resin, is fixed to the quarter panel  10   b  in conformance with the curved portion  13   a  of the center rail  13  immediately below the curved portion  13   a . The cable guide  43  restricts contact of the closing operation cable portion  33 A, which extends at the lower side of the center rail  13  in conformance with the shape of the center rail  13  including the curved portion  13   a , with the quarter panel  10   b . That is, the closing operation cable portion  33 A slides along and contacts the cable guide  43  to change directions at the curved portion  13   a  without contacting the quarter panel  10   b.    
     As shown in  FIG. 4 , a rear side case  46 , which is formed from, for example, a resin, is fastened to the quarter panel  10   b  facing the rear end of the straight portion  13   c  of the center rail  13  at the rear of the straight portion  13   c . A grommet  47 , which is formed from, for example, resin, is fitted to the rear side case  46 . The rear side case  46  rotationally accommodates the rear pulley  18 , and the grommet  47  guides the rear cable  34  (opening operation cable portion  34 A), which is directed toward the front after changing directions at the rear pulley  18  in the rear side case  46 , to the interior of the center rail  13 , that is, the exterior of the vehicle. 
     The operation of the vehicle door opening/closing device will now be described. 
     First, when the drum  32  is rotated and driven in a forward direction by the drive motor  31 , the front cable  33  is wound and the rear cable  34  is unwound. This moves the guide roller unit  16 , which is coupled to the end  37 , toward the front along the center rail  13 , and the sliding door  20 , which is coupled to the guide roller unit  16 , is integrally moved toward the front. That is, the closing operation is performed. The end  37  is coupled to the guide roller unit  16  at the rear (front cable coupling portion  28 ) of the load roller  22 . This accordingly separates the end  37  and the front cable coupling portion  28  at the fully-closed position from the front pulley  17 . Thus, a sufficient clearance between the end  37  of the closing operation cable portion  33 A and the front pulley  17  is obtained without increasing the amount bulged into the passenger compartment of the area accommodating the front pulley  17  at the front side of the inclined portion  13   b  of the center rail  13 . 
     When the drum  32  is rotated and driven in the reverse direction by the drive motor  31 , the rear cable  34  is wound and the front cable  33  is unwound. This moves the guide roller unit  16 , which is coupled to the end  38 , toward the rear along the center rail  13 , and the sliding door  20 , which is coupled to the guide roller unit  16 , is integrally moved toward the rear. That is, the opening operation is performed. 
     As described in detail above, the present embodiment has the following effects. 
     (1) The closing operation cable portion  33 A of the front cable  33  is located at the outer side and the lower side of the center rail  13 , and the end  37  is coupled to the front cable coupling portion  28  of the guide roller unit  16  at the rear of the load roller  22 . Accordingly, the end  37  of the closing operation cable portion  33 A and the front cable coupling portion  28  at the fully closed position are separated from the front pulley  17 , which is located at the front of the end  37 . Thus, a sufficient clearance is obtained between the end  37  of the closing operation cable portion  33 A and the front pulley  17  without increasing the amount bulged into the passenger compartment of the area accommodating the front pulley  17  at the front side of the inclined portion  13   b  of the center rail  13 . This limits reduction of the space in the passenger compartment and limits deterioration in the appearance of the trimming  50 . Further, in a vehicle including three rows of seats such as a van, a minivan, and the like, the ease to enter and exit the vehicle from the seat in the third row is unaffected. 
     (2) The end  37  of the closing operation cable portion  33 A is arranged proximate to the end  38  of the opening operation cable portion  34 A as viewed from above. Accordingly, the two ends  37  and  38  of the closing operation cable portion  33 A and the opening operation cable portion  34 A, as well as the front cable coupling portion  28  and the rear cable coupling portion  26 A are arranged in a concentrated manner. This allows for the guide roller unit  16  including the base plate  21  to be further reduced in size as viewed from above. 
     (3) The end  38  of the opening operation cable portion  34 A is coupled to the guide roller unit  16  from the extending direction of the rear cable  34  (opening operation cable portion  34 A), which extends to the end  38 , that is, a direction (vehicle widthwise direction) that differs from the direction in which tension acts on the rear cable  34 . This improves the ease for coupling the rear cable  34 . 
     In the same manner, the end  37  of the closing operation cable portion  33 A is coupled to the guide roller unit  16  from the extending direction of the front cable  33  (closing operation cable portion  33 A), which extends to the end  37 , that is, a direction (vehicle vertical direction) that differs from the direction in which tension acts on the front cable  33 . This improves the ease for coupling the front cable  33 . 
     (4) The rear cable coupling portion  26 A, to which the end  38  of the opening operation cable portion  34 A is coupled, is coaxial with the rear vertical roller  23 . Accordingly, the rear cable coupling portion  26 A and the vertical roller  23  are arranged in a concentrated manner. This allows the guide roller unit  16  including the base plate  21  to be further reduced in size as viewed from above. In particular, the number of components may be reduced since the support pin  25  of the vertical roller  23  is integrally formed with the rear cable coupling portion  26 A. 
     (5) The rear cable coupling portion  26 A is inserted into and received in the separation stopper  38   b , which is fitted into the holder  38   a  of the end  38 , so that the end  38  is not separated from the rear cable coupling portion  26 A. 
     (6) The cable guide  43  is arranged in conformance with the curved portion  13   a  of the center rail  13 . This allows for a reduction in the consumed amount of material compared to, for example, when the cable guide extends over the entire length of the center rail  13 . 
     The present embodiment may be modified as described below. 
     The separation stopper  38   b  of the end  38  may be formed from metal. 
     The end  37  of the front cable  33  may be formed by a holder and a separation stopper like the end  38  of the rear cable  34 . Alternatively, the end  38  of the rear cable  34  may be formed like the end  37  of the front cable  33 . 
     At least one of the ends  37  and  38  may be hook-shaped. Further, the ends  37  and  38  may have any shape as long as the ends can be coupled to the guide roller unit  16 . For example, the ends  37  and  38  may be shaped so that they are coupled to the guide roller unit  16  by pulling the ends  37  and  38  in the direction in which tension acts on the closing operation cable portion  33 A or the opening operation cable portion  34 A. 
     The rear cable coupling portion  26 A, to which the end  38  of the opening operation cable portion  34 A is coupled, does not have to be coaxial with the rear vertical roller  23 . 
     The end  37  of the closing operation cable portion  33 A does not necessarily have to partially overlap the opening operation cable portion  34 A as long as closing operation cable portion  33 A is arranged proximate to the end  38  of the opening operation cable portion  34 A as viewed from above. 
     The closing operation cable portion  33 A of the front cable  33  may be arranged at the upper side of the center rail  13 . 
     Two cables, the front cable  33  and the rear cable  34 , are used. Instead, a single cable may be used. In this case, one end of the cable corresponds to the end  37 , and the other end corresponds to the end  38 .

Summary:
A front cable and a rear cable are wound about a drum, are made to change direction by being caught onto a front pulley and a rear pulley, respectively, disposed on a center rail, and are respectively connected to a guide roller unit at respective terminals. The closing cable section of the front cable is routed to the outside of the center rail, the corresponding terminal being connected to the guide roller unit farther rearward than a load roller, and the opening cable section of the rear cable is routed to inside the center rail, the corresponding terminal being connected to the guide roller unit.